Nextcloud 18.0.4 unable to communicate with collabora

Hi, after an upgrade from nextcloud 17 to 18.0.4 collabora is not longer working. In my server ubuntu 18.04.4 I have nginx as a reverse proxy, collabora/code (latest) inside docker and latest collabora app.
For what I understand collabora docker looks good:

curl -k https://localhost:9980/hosting/capabilities

{“convert-to”:{“available”:true},“hasMobileSupport”:true,“hasTemplateSaveAs”:false,“hasTemplateSource”:true,“productName”:“Collabora Online Development Edition”}

curl -k

{“convert-to”:{“available”:true},“hasMobileSupport”:true,“hasTemplateSaveAs”:false,“hasTemplateSource”:true,“productName”:“Collabora Online Development Edition”}

docker container logs reports:
wsd-00008-00037 2020-05-27 13:29:27.444406 [ websrv_poll ] ERR Socket #26 SSL BIO error: closed unexpectedly (-1). (0: Success)| ./net/SslSocket.hpp:278
wsd-00008-00037 2020-05-27 13:29:27.444636 [ websrv_poll ] ERR Error while handling poll for socket #26 in websrv_poll: SSL Socket closed unexpectedly.| net/Socket.cpp:308

I have no relevant errors in nginx log, while in netcloud log I have lots of:
{“reqId”:“o6yXU8KO2YW1udsvb0tg”,“level”:0,“time”:“2020-05-27T15:29:23+02:00”,“remoteAddr”:“”,“user”:“admin”,“app”:“no app in context”,“method”:“GET”,“url”:"/ocs/v2.php/apps/notifications/api/v2/notifications",“message”:“Deprecated event type for OCA\User_LDAP\User\User::postLDAPBackendAdded: null”,“userAgent”:“Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:76.0) Gecko/20100101 Firefox/76.0”,“version”:“”}

any clue?
Thank you


I guess you use richdocuments-3.6.0. Maybe this post can help you.

Edit: fixed wrong link

Thank you Thom1 for your suggestion, this was not really my case but after some trying I was able to solve.
Looks like solutions are variable and for me does work reverting richdocuments to 3.5.0 (3.5.3 still does not work), while other found workarounds in WOPI, reverse proxy configuration and so on.

Best regards