OX-Documents doesn't work unter 4.4-7

With the newest version of OX-Documents (v. 7.10.4-ucs1) and UCS (4.4-7) we have one problem. If I open an existing document a new tab opens and then OX-Documents is loading forever…

grafik

Nothing else than this loading-symbol, no matter if I wait 10min or 1 hour.
Sometimes it says the document is very large, so it could take a few minutes, but same here.
grafik

Nobody has any idea or maybe a guess?

is the document-converter service running?

Yes the service “open-xchange-documentconverter-server” is running!

image

Any other ideas maybe? I cant find anything which could it be…also no logs…

Are the ceritificates ok?
(Letsencrypt seems not work fine at the moment - see System-diag)