I figured as much. Will try to produce a matching triple of both logs and a save file on thursday.

For now, on my current attempt I have noticed that the issue seems to be linked to screen resolution.

I played the previous games on:

• fullscreen 1920x1080
• fullscreen 1920x1080
• fullscreen 1920x1080
• windowed 1600x900

The first three games exhibited the bug earlier than the fourth one, but at that time I had put that down to random chance.

Today I played My Pet Dungeon level 1 on

• fullscreen 1280x720

and was unable to reproduce the bug within the ~two hours it took me to beat the level.

Still reproducible:

• Windows
• 10 Professional
• 64 bit
  • 8 Gb
  • Intel Core i7-6500U
  • nVidia GeForce 940M
• v1.6.3 (Steam version, installed yesterday)
• main Campaign level 2, in a total of 5/5 attempts.
• 3 output logs, numbered as following:
  • 0 - out of the box
  • 1 - after following "Missing, Invisible or Lagging UI" case 1
  • 2 - after following "Missing, Invisible or Lagging UI" case 2 and reducing graphic options to minimum
  • Each game has been cancelled via Alt+F4 as soon as the bug was noticed.
  • Each game there was UI - only UI - lag visible as much as 1 minute before the bug occured.
  • The game itself runs smoothly and even somewhat too fast (judging by animation speed).
  • Save files were not generated. Each game was started from the Campaign menu.
  • the logs on DropBox

For reference: My machine is an unmodified Asus X555U laptop.

Interestingly, I was unable to reproduce this effect in Campaign level 1.

... Also reproducible in My Pet Dungeon level 1. Seems to consistently happen soon after the 10 minute mark.

• 10 minute saves of both levels on DropBox
  

... Sadly reloading a save game seems to postpone the occurence of the bug. It might be possible to restart the game every ten minutes to stave it of indefinitely - of course, this does not allow to actually enjoy playing it.