My infill was 25%. Like I said, other than the same exact spots cracking off from 2 different i3 printers and 3 different filaments, it just seems like those areas are a problem.. The good news is, I was at least able on the last one to glue on the ends for cosmetic only and at least show my little guy.
It's the end of the hinge arms,, the u shape breaks off at the dowel - same on all of them. I'll upload pics later they look absolutely beautiful otherwise. If I had layer separation or other under extrusion etc. I'd lean more towards that....but that's why I spun up on the other i3 printing 20c higher on totally different filament, just to rule out whether it was machine/user error. :)
I wonder how many others are just so elated to get the thing to crank open that they are just maybe silently living with those ends breaking off and just not reporting it here so you are aware. My last one seems to function pretty good minus the broken ends because I'm not really putting any weight on it so also perhaps some folks have them break off at time of initial opening too and just aren't even aware of it.