Note that this isn't meant to be an exhaustive compendium of all possible issues encountered in Tarkov. It is simply meant to shed some light on some of the most widely reported instances.
The infamous "full auto glitch"
This one is commonly brought up but surprisingly rarely discussed. One frequent similarity between cases is that users are single-tapping their guns in full auto mode, then caught off guard when their gun stops working when they hold down the trigger once Jules is finished reciting Ezekiel 25:17 and it's crunch time.
If this sounds familiar, this is actually because the way that Tarkov categorizes inputs. There are 3 types for all actions and mappings: single keypress, double keypress, and continuous keypress. These three are all distinct and never overlap in how the game accepts combinations of them. Any input goes to one of the three options and cannot be shared.
For weapon fire mappings, when a gun is in full auto mode and you input a single keypress (usually LMB), it shoots exactly one bullet, as long as you release the keypress before the next shot. If you hold down the keypress, it fires full auto continuously until you let go of it.
What's happening here is that players are tapping twice in quick succession within their preset double-click interval and the game is registering it as a "double keypress" and outputting the double-keypress assignment without regards to whether the second press gets held down or not. The game automatically maps the "double keypress" as 2 single taps by default and stops there.
You can try this in the hideout shooting range. If you tap 3 times in quick succession and hold the last one, full auto will work fine. This is because the game interprets it as 1x[double click] + 1x[sustained click] = 3 single taps then full auto. If you tap 4 times in quick succession and hold the last one, full auto will not work because the game interprets it as 2x[double click] = 4 single taps and done.
We can argue whether we like this design or not. Personally I think it's interesting because it allows for various unique/flexible mappings. I map my combat reload to single-press R (where you drop the mag) and standard reload to double-press R (where you take extra time but keep the old mag) – the idea here being that if I have the time to do a longer reload, I have the time to press R an extra time.
You could also map scope toggle to single-click, tactical laser toggle to double click, and your actual scope ADS as continuous, all to RMB with different input sequences and they would never conflict with each other.
The point is simply to raise awareness of this mechanic so that if you're planning on full autoing after several single-taps, be prepared to click 1 extra time. Most people attribute this to another symptom of broken client-server interactions but this instance is actually just the nature of the way Tarkov categorizes inputs.
This one is also widely reported and frequently combined with video footage of a person emptying an entire mag of ammo to apparently no effect. This is caused by server-client desync issues that occur not during the gunfight, but during the magazine reloading input. What happens here is that the input to reload your gun does not make it to the server, which means that on your client it shows a fully reloaded gun, while the server thinks you are running around with an empty magazine loaded.
Tarkov tracks gun states on client separately from the server, which means that your client will assume everything is fine and when you pull the trigger, bullets will come out, impact marks are rendered, blood splats, etc.
All of these are client-side renders. In reality, the server does not recognize any bullets being fired (as you never loaded them) and if you have a squadmate, all they'll hear is your clicking as you fire an empty gun. Assuming you die after something like this, always check the Ammo Used section in the death screen recap to see if the server is recognizing the same number of shots as you would have expected. If you didn't use the ammo, it means you loaded a ghost magazine.
This is definitely related to server desync and game engineering mechanics, but with most things in Tarkov, severely exacerbated by user-side internet issues and hardware limitations. When running Tarkov on my old and new PC, I might see artifacts of server desync 2-3 times an hour on my old system, while on my new system I might see those artifacts 2-3 times a month. Tarkov is not fully optimized, and when your system needs to reallocate resources on the fly, it significantly widens the window for desync errors to occur.
Goal here is not to victim blame those that suffer from these issues, as there are some people that do have high end rigs that still run into problems. The only point is that it is possible to have a consistent gameplay experience, so don't lose hope – upgrade what you can, keep your drivers up-to-date, etc. (See next section for more details)
Screen freezes/pauses/map stutters
The most common culprit here is typically lack of memory, or client computer RAM. The game is trying to reshuffle limited resources mid-raid and the client simply stops bothering to give updates to your computer outputs while it figures things out. I will recommend a bare minimum RAM of 16GB to run Tarkov, and if you're sitting at 16GB I highly recommend shutting off all other non-Tarkov applications like Discord, Chrome, etc. Open maps on another device, or if you must, use a system tracker to check your RAM usage while running concurrently with other apps like Discord.
If you are on 8GB or less, you are going to be forced to use the game's auto RAM cleaner (in the settings) – this is a last resort and only for those with limited RAM. Definitely turn off all other applications.
This I'm not 100% on, but the rumor is that the game operates best running on only physical cores for Intel, but the opposite for AMD – I'll let others chime in if they have better sources.
Bottom line on tech specs:
I can't give you threshold for stable performance as I have only ever used two setups, but I can give an example for how two rigs performed.
With my latest rig running the latest gen Intel 10700k, RTX 2080 Ti I see about 2-3 server desync artifacts maybe a month, and silky smooth client performance. Game is actually very stable and tech issues are very rare. If this was the only rig I ever played on, I would never believe people blaming lag, etc. because I almost never see it, and is just as stable as fully released games like Apex Legends, Valorant, CS:GO, etc.
My old rig, running Intel 6500k with GTX 1070 and only 8GB of RAM, I saw about 2-3 server desync artifacts an hour and constant screen freezes (4-5 seconds of freezing every 60 seconds or so) depending on the map. Factory was generally fairly smooth, while Interchange was unplayable as a the game would stutter long enough for a scav to slowly tickle me to death with a buckshot shotgun from 50m away. Game was borderline unplayable in that there was only 2-3 maps that were semi-reliable at best. If this was the only rig I played on, I would think that the game isn't even ready for Alpha because it barely even runs at all and half the maps don't work.
Hopefully this gives some context on different experiences you might have and where those root issues might be.
I'm NA-East based and server ping is always less than 30. ~1GB upload/download with fiber internet. Typically 0% packet loss.
I've never tested spotty internet connections but assume this could also have just a bad an impact for those with spiking ping, packet loss, slower connections, etc. I just can't speak to it as I only have 1 internet setting ever used.
Let me know if these threads are helpful. I've been thinking of making another one that discusses what type of gear is helpful to optimize Tarkov experience in-game.