How did you switch the agent to The MovieDB? Via Fix Match or changing the agent in your library settings? If the latter, you’ll likely need to perform the Plex Dance to complete the switch:
As far as I know, changing the agent for the library only affects newly added content. Existing content will continue to use the agent which with it was originally matched.
It will probably be easier for you to use Fix Match and select The MovieDB in the Search Options.
