Rob_C Same little tray prints cleanly in the middle, but the front right corner has gaps. I was about to start changing every first-layer setting.
rlopez Before changing the profile, clean the plate using its manufacturer instructions and check that it is seated properly. One corner behaving differently is a useful clue.
cpalmer Also inspect underneath the plate. A tiny bit of plastic trapped there can be surprisingly annoying.
Rob_C Found a little scrap underneath it. Cleaned and reseated the plate, reran levelling, and the test patch is even now.