Our work has now been completed!
Tasks Performed:
Updated all containers to the latest versions.
Split the existing Docker Compose file into separate stacks for better manageability.
Enabled updating of all media-related containers to the latest version via the Portainer UI (see guide below).
Fixed a permission issue in Sonarr that was preventing content imports.
Implemented a script to set correct permissions on each server reboot to prevent future issues.
Fixed an issue where Cockpit couldn't check or update Ubuntu from the Web UI.
Installed all pending Ubuntu updates.
Removed unused Docker images to free up space.

We have identified intermittent issues with importing episodes. Originally, we thought this was only affecting the automatic importation; however, we're unable to import these manually, either.

We're now reviewing, troubleshooting and implementing a fix.