I recently moved my TV show library to a folder off of my media root folder so I can just keep my movies in their own folder. I was careful to make sure the locations the library pointed to contained both file paths until everything was moved over.
That being said, Plex had to go back through and re-generate video previews, detect intros and 9 days later, it is still detecting credits.
The yellow circle is pretty good for individual tasks that do not take much relative time. However, the long-term things would be more interesting if I could tell that 9,000 TV shows needed to be detected and we are on 6,413 with 587 left to go, and maybe a projected time until the job is done.
That way, should I have to do maintenance, such as applying a system update, I could roughly know how long I should wait until this can be done without interrupting Plex in doing its background tasks.
I do see on my Synology that system utilization has been getting up into the 90s as each file is examined, and between CPU goes down, so a pulse pattern on the CPU, so I know it is working.