Can't download File from groupfolder


I 've uploaded an existing excel file to a new created groupfolder.
And now (12h later) I cant open it with onlyoffice and I cant download, copy, move or delete the file.
I get the following messages when i try to download the file.
Internal Server Error
Technische Details
Entfernte Adresse:
Anfragekennung: PjZWl4NXmm7560AzRJEK
Nextcloud – ein sicherer Ort für all Deine Daten

where can I found what happend? I can access the file via shell.

thx shb