My Claws-mail plug-ins had all been removed. It was no problem to reload them into Claws, as they were all still available.

The other thing was that the user interface had a couple of glitches. When the cursor moved over icons in the tool bar, all of the icons to the right moved slightly to the left! Also when I went to compose a message, the area where you set up the recipients usually is able to display about 4 lines of recipients and the icon to the right is of a brush, which is for clearing that line. After the upgrade the space for each line was much deeper, so that only 2 lines would fit in the area I had allocated.

The part where icons jump a little to the left rang a bell in my head and I thought it was something to do with themes.
I use lxdm and lxqt with Openbox. When I look in Preferences>Customise Look and Feel, the Widget option includes Clearlooks-Phenix-Sapphire, which I selected, as well as the Window Border>Theme also offers Clearlook-Pheneix-Sapphire, which I also selected. Once this theme had been selected, the UI oddities, mentioned above, went away.

There is some discussion about Clearlooks-Phenix-Sapphire in the Devuan thread.

Geoff