Thanks for playing and reporting the bug, I was able to reproduce the issue! I found out it was not limited to Wildfire, could happen as soon as there were two identical marks under the same stone for an effect that needs to happen only once per stone. I uploaded a patch: version 0.1e fixes it. Also, I replaced Wildfire marks with attack marks for the encounter on the screenshot. Wildfire needs a range, so I realized it was actually doing nothing for most stones...
Yes, the game auto-saves at the beginning of each turn, so players can almost always recover and continue their game even if it softlocks during the effects triggers :)
As for the arrow, does that mean I should increase the hidden tier of the Fleeting effect? That would make arrows more expensive in the shop.