Matching with the Movie Database agent doesn't work?

I’m pretty sure it’s not the router. had it for over a year and I didn’t change any settings on it. Other stuff in my network has no issues.
Disabled IPv6, but that also didn’t help. My ISP supports native IPv6, so I have it enabled on my network, laptops and servers.
Dragging also didn’t solve the issue. In fact, it is now not downloading some of the artwork from The TVDB, for example for NOVA (which definitely has artwork). Matching for the TVDB works just fine. It did download artwork for The Shannara Chronicles.
The “ERROR - Error issuing curl_easy_perform(handle): 28” messages persist.

Just to be sure; this is my docker-compose for PMS:
plexms: container_name: plexms restart: always image: plexinc/pms-docker network_mode: host volumes: - ${USERDIR}/docker/plexms:/config - ${USERDIR}/Downloads/plex_tmp:/transcode - /mnt/Media/Movies:/media/Movies:ro - /mnt/Media/TV:/media/TV:ro - ${USERDIR}/docker/shared:/shared ports: - "32400:32400/tcp" - "3005:3005/tcp" - "8324:8324/tcp" - "32469:32469/tcp" - "1900:1900/udp" - "32410:32410/udp" - "32412:32412/udp" - "32413:32413/udp" - "32414:32414/udp" environment: - TZ=${TZ} - HOSTNAME="MyPlexServer" - PLEX_CLAIM="claim-xxxxx" - PLEX_UID=${PUID} - PLEX_GID=${PGID} - ADVERTISE_IP="http://192.168.0.90:32400/"
Running the above config without network_mode in host causes Plex to lose the remote access connection.
Server: Ubuntu 18.04 with latest (nightly) Docker-CE build with PMS 1.13.0.5023.
I have similar issues on my old server which is an Arch Linux box (up-to-date) with the same PMS version.