I had the same problem many times when i first started playing. I found a way to fix the problem. It takes a few min though. All you have to do is totally unequip all gear everything then change loadout and put back on the gear then resave.
You can also try right click everything and select "apply to all loadouts" then do the same on your mounts page. If it still doesn't work, try removing the items from your potion tray.
Try the "save to all loadouts" trick for your companions first. If that doesn't work, then try it for mounts. If it still doesn't work, then try appearance. It usually the companion settings that cause the problem in my experience, so the first step will likely be enough.
It normally applies to an artifact you changed or recycled for refinement. It only happened to my warlock once. I placed all the items into inventory from the first page. Once stripped down, then I was able to make the switch.
Answers
I hope that might help.