It looks like the issue is actually with ejabberd PubSub/PEP implementation which just decided no to send last published item when it receives storage:bookmarks+notify with a set of features supported by the client. This is against the PEP specification which states:

When a PEP service receives initial presence [13] from a subscriber's resource including XEP-0115 information that indicates an interest in the data format, it MUST generate a notification containing at least the last published item for that node and send it to the newly-available resource; see below under Sending the Last Published Item.

I'm adding a workaround for the in the client library when I will be aware that we have connected to buggy ejabberd server.

@andrzej.wojcik - have you reported this to ejabberd? Maybe cooperating with them and including proper fix in their implementation would be a good idea (and Holger seems to be quite cooperative)

I thought about it but in the end, I've ended up with a workaround as roll-out of a fix will take some time either way.

Yes, it will take time but I think that having fixed something instead of adding workarounds for bugs is better. I'll take care of that.