Hello Ike,
I searched my print history and this is what I found out :
I did only one print with this resin and it was a failure.
After this, I reverted to the good old blue tough resin and managed to do my parts.
I don’t remember exactly what failed, but I admit I was stretching it with those almost vertical disks, all bunched-up.
I took out the bulk of the failed print, but probably didn’t see the few cured layers that had stuck to the tank.
Since I put the tank in a carton and in a closed cabinet, there could have been no light entering the vat after that.
I guess the mystery is solved.
Not too sure about “Tough 1500” though ; I noticed that it’s components had a tendency to separate (translucent goo / grey gunk) like some cheap resins I had tried in the past.
I’ll have to do more tests with easier to print parts, as soon as I can get my belt issue sorted.
Sorry for scaring everybody with the resin monster ; I should have checked my dashboard before posting.