AdGuard Docker und Unraid Host recently showing upstream errors

Hi everyone,
first of all I'd like to say thank you for this great piece of software that I've been using for years now. Never really had any issues until recently. Not even sure whether this is actually an AdGuard problem but my troubleshooting only got me so far.

Everything has been restarted including the host machine. The logs of my AdGuard docker show the following:

`
[...]
2024/01/08 09:54:43.780570 [error] dnsproxy: upstream https://dns10.quad9.net:443/dns-query failed to exchange ;entitlements.itunes.apple.com. IN HTTPS in 30.002366628s: requesting https://dns10.quad9.net:443/dns-query: Get "https://dns10.quad9.net:443/dns-query?dns=AAABAAABAAAAAAABDGVudGl0bGVtZW50cwZpdHVuZXMFYXBwbGUDY29tAABBAAEAACkIAAAAgAAAAA": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
2024/01/08 09:54:43.780641 [error] dnsproxy: upstream https://dns10.quad9.net:443/dns-query failed to exchange ;entitlements.itunes.apple.com. IN A in 30.002379945s: requesting https://dns10.quad9.net:443/dns-query: Get "https://dns10.quad9.net:443/dns-query?dns=AAABAAABAAAAAAABDGVudGl0bGVtZW50cwZpdHVuZXMFYXBwbGUDY29tAAABAAEAACkIAAAAgAAAAA": net/http: request canceled (Client.Timeout exceeded while awaiting headers)
2024/01/08 09:54:43.887866 [error] dnsproxy: upstream https://dns10.quad9.net:443/dns-query failed to exchange ;s3-w.us-east-1.amazonaws.com. IN AAAA in 30.001926293s: requesting https://dns10.quad9.net:443/dns-query: Get "https://dns10.quad9.net:443/dns-query?dns=AAABAAABAAAAAAABBHMzLXcJdXMtZWFzdC0xCWFtYXpvbmF3cwNjb20AABwAAQAAKQgAAACAAAAA": net/http: request canceled (Client.Timeout exceeded while awaiting headers)
2024/01/08 09:54:43.887909 [error] dnsproxy: upstream https://dns10.quad9.net:443/dns-query failed to exchange ;alive.github.com.IN A in 30.002037792s: requesting https://dns10.quad9.net:443/dns-query: Get "https://dns10.quad9.net:443/dns-query?dns=AAABAAABAAAAAAABBWFsaXZlBmdpdGh1YgNjb20AAAEAAQAAKQgAAACAAAAA": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
[...]`

Some dns requests go through, so that my AdGuard dashboard shows the following:

Host Machine:
- Unraid 6.12.6
- Ryzen 516GB
- AMD Ryzen 5 1600X Six-Core @ 3600 MHz
- AdGuard running on br0 Network interface

Can you guide where to look at or how to troubleshoot? Interestingly, nothing on my config changed and in the past weeks I had this issue occasionally but a host reboot solved it (temporarily).

Thanks a lot.