I have been having the same problems for 1-2 weeks. The client disconnects every 10-20 minutes with the same error message. At least for me it seems to be the server or the authentication process, because otherwise I have no network problems.
I can confirm the same issues. In the last ~6months, I had several disconnects with the same behavior:
Starting with disappearing of all AI aircraft from MSFS (you can see it as well in Little Nav Map).
Voice server is still working fine.
When reconnecting most of the times a connection is established, but aircraft are not reappearing and all ATC stations in the vPilot list are not listed. Lists are just empty. Voice connection is working.
When reconnecting different error messages appear in vPilot (see log).
After a couple of reconnects aircraft and ATC stations are coming back.
Most of the times the issue starts again after 2-3min.
It appears most of the times in the last third of the flight in the approach and landing phase.
Here an example log of today from LOWI-EDDM:
2024-05-08 19:40:32.778 +02:00 [INF] vPilot version 3.9.0 starting up
2024-05-08 19:40:32.791 +02:00 [INF] Running in "Standalone" mode
2024-05-08 19:40:32.925 +02:00 [INF] Licensed for non-commercial entertainment use only
2024-05-08 19:40:33.922 +02:00 [INF] Downloaded 1 servers
2024-05-08 19:40:34.362 +02:00 [INF] Validating "Msfs"
2024-05-08 19:40:36.389 +02:00 [INF] Aircraft config paths hash is different
2024-05-08 19:43:17.305 +02:00 [INF] Custom model matching rules loaded.
2024-05-08 19:43:17.879 +02:00 [INF] Model matching rules generated.
2024-05-08 19:43:17.896 +02:00 [INF] "FbwVpilotActive" value changed: false
2024-05-08 19:45:46.764 +02:00 [INF] Connecting to network
2024-05-08 19:45:46.786 +02:00 [INF] Connected to network
2024-05-08 21:22:35.103 +02:00 [INF] Disconnected from network
2024-05-08 21:23:11.411 +02:00 [INF] Connecting to network
2024-05-08 21:23:11.431 +02:00 [INF] Connected to network
2024-05-08 21:25:40.196 +02:00 [INF] Disconnected from network
2024-05-08 21:25:51.083 +02:00 [INF] Connecting to network
2024-05-08 21:25:51.103 +02:00 [INF] Connected to network
2024-05-08 22:02:54.834 +02:00 [ERR] Network error: The server has failed to respond to the authentication challenge.
2024-05-08 22:02:54.834 +02:00 [ERR] Disconnected from network
2024-05-08 22:02:59.888 +02:00 [INF] Connecting to network
2024-05-08 22:03:00.934 +02:00 [INF] Connected to network
2024-05-08 22:03:13.903 +02:00 [INF] Disconnected from network
2024-05-08 22:03:18.701 +02:00 [INF] Connecting to network
2024-05-08 22:03:18.738 +02:00 [INF] Connected to network
2024-05-08 22:05:17.507 +02:00 [INF] Disconnected from network
2024-05-08 22:05:22.432 +02:00 [INF] Connecting to network
2024-05-08 22:05:24.509 +02:00 [INF] Connected to network
2024-05-08 22:05:24.549 +02:00 [ERR] Network error: Parse error. (Raw packet: N:N311CV:5433:1:47.43896:12.39219:27245:238:425721$DISERVER:CLIENT:VATSIM FSD V3.43:0f1cace0d2cc46b50c1a70)
2024-05-08 22:05:35.199 +02:00 [INF] Disconnected from network
2024-05-08 22:05:38.935 +02:00 [INF] Connecting to network
2024-05-08 22:05:38.972 +02:00 [INF] Connected to network
2024-05-08 22:07:27.109 +02:00 [ERR] Network error: EndReceive failed: (10054) An existing connection was forcibly closed by the remote host
2024-05-08 22:07:27.114 +02:00 [ERR] Disconnected from network
2024-05-08 22:07:31.300 +02:00 [INF] Connecting to network
2024-05-08 22:07:32.342 +02:00 [INF] Connected to network
2024-05-08 22:07:34.686 +02:00 [INF] Disconnected from network
2024-05-08 22:07:38.158 +02:00 [INF] Connecting to network
2024-05-08 22:07:38.194 +02:00 [INF] Connected to network
2024-05-08 22:08:43.190 +02:00 [INF] Disconnected from network
2024-05-08 22:08:47.897 +02:00 [INF] Connecting to network
2024-05-08 22:08:47.940 +02:00 [INF] Connected to network
2024-05-08 22:08:49.640 +02:00 [INF] Disconnected from network
2024-05-08 22:08:52.825 +02:00 [INF] Connecting to network
2024-05-08 22:08:52.862 +02:00 [INF] Connected to network
2024-05-08 22:09:12.589 +02:00 [INF] Disconnected from network
2024-05-08 22:09:17.383 +02:00 [INF] Connecting to network
2024-05-08 22:09:17.419 +02:00 [INF] Connected to network
2024-05-08 22:12:18.122 +02:00 [ERR] Network error: Client authentication response timeout
2024-05-08 22:12:21.157 +02:00 [ERR] Network error: EndReceive failed: (10054) An existing connection was forcibly closed by the remote host
2024-05-08 22:12:21.157 +02:00 [ERR] Disconnected from network
2024-05-08 22:12:30.174 +02:00 [INF] Connecting to network
2024-05-08 22:12:31.212 +02:00 [INF] Connected to network
2024-05-08 22:13:31.259 +02:00 [ERR] Network error: The server has failed to respond to the authentication challenge.
2024-05-08 22:13:31.259 +02:00 [ERR] Disconnected from network
2024-05-08 22:13:35.399 +02:00 [INF] Connecting to network
2024-05-08 22:13:35.434 +02:00 [INF] Connected to network
2024-05-08 22:13:35.753 +02:00 [ERR] Network error: Parse error. (Raw packet: WAT4203:48.3487600:11.7784500:1482.97:9.18:4191784:5.0907:0.0001:-6.4233:-0$DISERVER:CLIENT:VATSIM FSD V3.43:121de51ef5d02a34)
2024-05-08 22:13:50.775 +02:00 [INF] Disconnected from network
2024-05-08 22:13:54.867 +02:00 [INF] Connecting to network
2024-05-08 22:13:54.910 +02:00 [INF] Connected to network
2024-05-08 22:14:05.761 +02:00 [INF] Disconnected from network
2024-05-08 22:14:10.738 +02:00 [INF] Connecting to network
2024-05-08 22:14:10.781 +02:00 [INF] Connected to network
2024-05-08 22:14:10.824 +02:00 [ERR] Network error: Invalid field count. (Raw packet: THY1379:49.1242700:12.2110900:28742.00:26554.13:4486740:135.4309:$DISERVER:CLIENT:VATSIM FSD V3.43:6bfd77a7330c6bcff30a)
2024-05-08 22:14:14.677 +02:00 [INF] Disconnected from network
2024-05-08 22:14:17.494 +02:00 [INF] Connecting to network
2024-05-08 22:14:17.531 +02:00 [INF] Connected to network
2024-05-08 22:16:42.338 +02:00 [ERR] Network error: EndReceive failed: (10054) An existing connection was forcibly closed by the remote host
2024-05-08 22:16:42.341 +02:00 [ERR] Disconnected from network
2024-05-08 22:16:50.165 +02:00 [INF] Connecting to network
2024-05-08 22:16:50.201 +02:00 [INF] Connected to network
2024-05-08 22:16:55.066 +02:00 [INF] Disconnected from network
2024-05-08 22:17:01.194 +02:00 [INF] Connecting to network
2024-05-08 22:17:01.238 +02:00 [INF] Connected to network
Similar to an old forum entry. Connecting from Germany without any VPN.