Category deseapears

Hi,

I installed Download Manager free for a client 2 month ago, it was working fine until few days.
I do not have a possibility to assign a file to file categories (working fine before).
There is no error and error log is fine.

The onlyway to assign categories, is to add categories with “fast modification” on post (not sure about my translation).
No way to assign while creating file.

Could you tell me what to do to repare it please ?

Thank you in advance for responses !
Regards