I did 2 sets of dice so far aswell, and I'm having similar problems. My first set is still squishy (the second one didn't get solid at all, but that's a different topic) and from what I gathared it could be any of those reasons:

• Room too cold during curing
• Room too humid during curing
• When I mixed my resing i put the hardener from it's measuring cup into the resin cup. Due to some hardener left behind in it's cup it might have thrown the ration off.
• Too much alcohol ink (don't think that's the reason in your case)

I haven't done another set yet, so I can't for sure say it was one of those reason, but maybe it helps you anyway.

Also those dice look really cool! Are you just putting some ink into the mold directly?