Are you sure that file upload was failing in 5.3.6-b181? I've detected this issue only in 6.0-b182 (it had changes in this area causing this issue) and this issue was resolved in 6.0-b183.

When I sent a message from BeagleIM then SiskinIM on the same chat shows Message was not encrypted for this device.

Is that on 1-1 chat or MUC? Are Beagle and Siskin connected to the same account? or one is sender and one is receiver of the message?

It is possible that this OMEMO issue can be caused by a bug in Siskin (it was bug in MartinOMEMO library). This issue was resolved there and build with this change was published as a beta version of BeagleIM while I'm still alpha testing a new version of SiskinIM with this change.

I am always on Beta and I copied the number from Beagle. I will not give my hand for that, however.

It was in 1-1 OMEMO encrypted chat. I was sending PDF contract file.