I update this post because on my test server, I've updated to 9.1.6. I'va got a message of integrity error.
In the details, I have the following :
_ - EXCEPTION_
_ - OC\IntegrityCheck\Exceptions\InvalidSignatureException_
_ - Certificate has been revoked._
The warning is only on the calendar which is part of Owncloud Core if my memory is good. I don't use an alternative claendar app that can be found in the old store.
The calendar is working but this warning distrub me.
So what should I do with this. Use another calendar app from the new market place or wait for the certificate to be updated ?