Issue with prints aligning properly

Hey all, newbie to the forums so forgive me if this is supposed to go somewhere else. I've been having an issue printing multiple parts for various prints and having them line up properly for assembly. For example, if I print the body and head separately (or even on the same plate) they will not line up properly when I go to put everything together. One part will always be slightly too big or too small. I have had this problem on many different files so I don't think that is the issue. I have had this problem on 3 separate printers (1 Phrozen Sonic Mini and 2 QIDI Shadow 5.5s). I am assuming this is an issue with resin printing itself but, given the insane level of detail they are capable of, I'm hoping it's something else. Any advice would be absolutely appreciated. Thanks and happy printing!