two people can't use my watchface, what do I do?

I wrote the "Another Mario" watchface and it has 789 downloads as of today.  I've been using it as my own watchface on my forerunner 935 for two years.  I've had two people say that it doesn't work at all for them.  One sent me a photo of his watch with the IQ with a yellow circle with an exclamation point.

Once in a while I get that too, but it is rare.  It always goes away on its own.  It hasn't done it in a while.  How do I troubleshoot this for those users?  The code for the face is really very simple.  It just shows HR, battery, time, date, and whether an alarm is set.

Thanks!