I had this issue for about a month and I couldn't find a fix until I tried this:
Download Intel's killer performance suite (I downloaded the beta and it worked) from here:
yes that is a real intel link not inteI (i), run it through
then when you boot it up, go to "prioritization engine", then applications, and find EscapeFromTarkov.exe and set its priority to 1, making it the most important application on your computer (you must have the game running to find it first) and hop into a scav raid to see if you disconnect!
Im pretty sure this issue is caused by a crowded computer with multiple applications using your WIFI, causing packet loss and disconnects. I hope this helped!
Source: https://www.reddit.com/r/EscapefromTarkov/comments/ql9htm/constant_server_connection_lost_fix/