I’ve updated my original post a little bit because it wasn’t completely accurate. Do you also experience the problem right after having updated from 4.0.1.45 to 4.0.1.48?
After I suddenly gained access again, I actually managed to just remove the unlocking attempts limit by following this post:
https://together.jolla.com/question/91297/how-to-recover-from-permanent-device-lock/
So, in case you also somehow manage to get into recovery mode again (I really don’t know what I did other than reboot into UI and recovery several times), the value you have to modify is ‘maximum_attempts’, just change it from 10 (or however many attempts you had configured) to -1, save and exit. Note that this probably doesn’t solve the underlying problem, but because it’s so weird and seemingly random, and the Jolla Tablet isn’t exactly Jolla’s main focus, I don’t think the problem itself will ever be fixed.