Someone removed there post so it makes it looks like I was talking directly to your first post.. sorry about that.
Someone mentioned it was probably due to dye ink, I stated the above. There have been many people on this site stating that dye ink is not any good for transfers when in fact I and others have had great success with it. While there may be some combinations that don't work, I do know I use dye ink with
JPSS and it works fine.
I would guess to say the above poster is correct in saying that it's a combination of heat temp and pressing times that may be causing your issue.
I'm using 375-380 for 30 seconds IIRC. I would guess that the cracking might be too much heat for too long of time maybe???