Connection Issue

My boyfriend keeps getting a “Connection Issue” error when joining my private server (I am the host). He connects successfully, plays for about 2-3 minutes, then disconnects with a connection error. When he reconnects, the same thing happens again after a few minutes. This occurs even if he is just walking around or idling - no specific in-game action triggers it. It started recently. We previously played in October without any issues. We took a break and returned on February 10th. Since then, the problem occurs inconsistently - some days it works fine, other days he disconnects repeatedly. No known update or specific event triggered it.
No mods installed and no game file modifications.
We did:
Verify integrity of game files via Steam;
Changed "CompressSaveFiles": true to "CompressSaveFiles": false in:
SteamLibrary\steamapps\common\VRising\VRising_Server\VRisingServer_Data\StreamingAssets\Settings\ServerHostSettings.json