Could you clarify a little what you think is happening? Is other device id removed from deviceslist of OMEMO PubSub node? or something else is happening?

I can confirm this part from mightyBroccoli: "Additionally Siskin does not request the keychain of a contact when starting a conversation". Way is dismail.de (Prosody) account with Siskin to conversations.im (ejabberd) account with conversations app

As for retrieval of contacts keychain (device id/bundle), it retrieves device keys only for devices that are listed on contact deviceslist and which is delivered by PEP (+notify).

Could you clarify a little what you think is happening? Is other device id removed from deviceslist of OMEMO PubSub node? or something else is happening?

Sure thing. My test device has various iOS XMPP clients installed, all connected with the same account. Which should result in a keychain containing a key for each device.

By removing clients for the equation I found that Siskin replaces the whole keychain when connecting. Which results in a "fresh" keychain, after the successful connection. I am unsure if this occurs every time siskin connects, but it happened quite often to be ux breaking.

By "fresh" keychain I do mean a keychain containing only siskins omemo key.

OK, it looks like this is the same issue as I've tracked down and fixed yesterday. New versions of Siskin IM and Beagle IM will have a fix for this issue.

That is awesome. Thank you for your effort.