ICEauthority related boot slowdown after recent update

Around the 1st of July I performed an update on my HP Elitebook 840 g1 running MATE 18.04. I think it was a kernel upgrade because it prompted a reboot. Afterwards, I got an error dialog saying "Could not update ICEauthority file /home/username/.ICEauthority" and the desktop wouldn't start. I went into the terminal and messed with the ownership and permissions of said file until the desktop booted - but incredibly slow, well over a minute instead of the usual instant startup.

I finally reinstalled because the machine was fresh from a few days ago anyway - I had only installed a couple of snaps, basically. However, after updating the freshly installed system, the desktop startup was slow again! But without ICEauthority dialog this time...

Any suggestions? I can't press escape to see the logs during boot for some reason.

Booting with the previous kernel worked. So, 4.15.0-24 is somehow causing this, and 4.15.0-20 is fine.

Any tips on how to gather enough information to report this issue?