There is a way of stopping the cracking , and that is to anneal the pex. Leave the cut parts in an oven at about 80c for 1 hr per mm thickness and let them air cool , this stress releives them.
Alternatively , use only cast acrylic with tensol glues. If you use extruded , use glues specific to extruded (Degussa makes many)
One can debur and scrape edges too , which does somewhat releive the problem.
How to tell whether its extruded or cast:
Burn a piece , extruded burns silently and will drip molten balls , cast burns with a crackly/smokey flame and wont drip.