Attack missed against equal AC

Level 10
2 weeks ago

I've got one 13 AC enemy left in the Tower of Magic (first?) Sorak fight.

My wizard casts a Fire Bolt. Rolls 12 + 6 (spell attack bonus) - 5 (3/4 cover) = 13.

Attack roll of 13 is supposed to hit against equal 13 AC. Yet, for some reason it missed.

Save file at the start of that combat:

Save file made right after this turn:

Game info: version 0.5.42 in Spring Hotfix Beta branch, Steam.

System info: Windows 7 (64 bit) SP1, Intel Core i5-4570, 16 GB RAM, GeForce GTX 1070, 1080p monitor.

Level 10
1 week ago

And again. So it's not a one-off.