I've noticed a bug in the modpack where items often get deleted in single player. On two separate occasions, I lost my backpack with all its contents, and another time, a shopping basket disappeared. Additionally, when I try to remove clothes and place them on the ground, they also get deleted. I have downloaded all of the content from the modpack, most of the others suggested by this post and don't have any other external mods. I don't rule out that I may have done something wrong myself, given the large number of mods to activate one by one, but I've done two checks and everything seems correct at first glance.