Hey BlueJ, thanks for your kind comment.
About your issue, I tested earlier on Chrome (Version 73) on Windows 10 (I don't have Chrome OS) and I was unable to reproduce the issue you mentioned (even if I click on the red monster when it is in front of any door). I often use Firefox, and with Firefox on Windows 10 I never had this problem either. Since I don't have the problem it's tricky for me to debug.
Do you encounter the issue always in the very exact same moment or does it seem to be random?
Could you please also tell me if the executable version also have this issue? You may download executables for Windows/MacOS/Linux.
Thanks