This glitch has been happening for awhile. I will set my inventory hotbar the way I find most convenient, but once I open a chest or any other screen that blocks my hotbar from visibility, I will return to find the hotbar scrambled. Then if multiple things get opened in a row, parts of my inventory will occupy multiple spaces in the hotbar. Below I included photos of my optimal hotbar, the first messed up hotbar, and the occupying multiple spots hotbar.