We just started a new world (completely new generated by the server, no pre-defined seed etc.) and the problem still happens.
Same issue for my 1.15.1 Vanilla Server. When trading glass panes with the cartography Villager, the server freezes and then crashes after about 30 seconds of freeze.
I have 4 crash logs attached to this comment.
Hope that helps.
Philip Zimmermann
We just started a new world (completely new generated by the server, no pre-defined seed etc.) and the problem still happens.