Nextcloud Client for Mac sync-error for some files

I have a Nextcloud-Client installed on a MBAir, with OS 10.14.5 and Nextcloud client 10.14.5 It synchronizes fine but today I added a new server and I get problems with three files:
I have no Idea why these 3 jpgs and the pdf
one jpg is 3,5 MB so it is not too big, the other one is quite big, 35 MB, and the pdf is 5 MB