Why Does My Kitten Keep Jumping In And Out Of The Litterbox?

My kitten will jump in and out of the litterbox. Sometimes he is actively trying to get in, but most of the time it’s a little leap or an accidental trip into the box that knocks him over. He does not do this every day – sometimes I’ll be gone for several days at a time and when I come home they usually have been going in and out of the litterbox without my noticing until they are getting sick from it! He has been diagnosed with UTD (unrecognized teratogen) so we don’t know what causes this behavior, but his vet thinks it might be linked to something during trimesters when cats have abnormal hormone levels. I’m looking for some insight on this behavior from anyone who may have experienced something similar!