sometimes either its that the chunks dont load for the pets or it doesnt update on the next tick at the right time but, after being on minecraft for like a long time for hours(not entirely sure how this happens), your pets dont respond to you. You make them sit and then you do stuff for like 7 hours, you save and quit, come back on the next day to find your wolf or cat or whatever wont allow you to right click on them so that they stand up.
????????????????
(no images necessary)

im guessing its because of the mods but even when i played it without mods it still happened. I am clueless