I assume we are talking about Movie Edit Pro 2021.
In which case if it's a fairly new install is a known issue here.
They should eventually turn up again after a while. MEP is known to continue building its library records for some time after shutdown for the first unknown amount of times of use. If the PC i shut down soon after using MEP it can start all over again.
It should eventually settle down but depending on how long you leave your pc on and working after using MEP the amount of time that takes could vary. I don't know if anyone here knows why this has changed but we have been warned by Magix that it can happen.