Errors similar to the following:

sonarrerrorpipeline GET /api/v3/queue/status: Expected query to return 1 rows but returned 0

can be fixed by going to System→Tasks, running the Housekeeping task and then restarting Sonarr.

Sonarr uses various online databases to pull metadata in order to be able to identify shows from various trackers. The online databases are voluntary work and sometimes do not get updated on time, such that when the database is not updated, Sonarr will fail to pull any episodes.

In order to make this issue better, the option Settings→Media Management→(Show Advanced)→Episode Title Required can be set to Only for Bulk Season Releases in order to allow Sonarr to import TV episodes that might have a "To be Assessed" (TBA) title.

For TV shows, this makes sense mostly because the individual title is not particularly important for episodes and the title can be updated later, even automatically, by Sonarr, contrasted to say the title of movie using Radarr.