Version: Android 1.1.1
I have attached 2 screenshots showing the bugs. Both occurred after I exited a mini-boss lair without fighting it.
The first shows the red X indicating that I am unable to extract cores, except that an extra one is drawn over the top left corner of the screen. It is persistent regardless of which monster my cursor is over when choosing which one to extract from.
The second shows a monster sprite stuck on the top left corner of the map. I can’t say for certain, but I am fairly sure that is the same sprite as the boss that I did not fight. The sprite was animated, but did not turn or change position. It could either be a graphical glitch, or the actual monster being spawned at that spot.