Was playing little Crusader for a while and had over (i think) 150k xp und also unlocked shield & sword milestone.
First never recieved the item and after log out and later log in again, every progress was gone.
Had this problem also with Halloween xp (think over 500k xp currently), and (i think) Plazaa/Arcade xp (don´t know exactly how much i lost there).
I only see sometimes in the right corner on top that it tries to “sync”, but that´s in an endless loop.
I know Steam bugged currently the whole system in here.
The status of issues with transactions, EXP, milestones, and achievements is being documented here: https://towerunite.statuspage.io/. More information can also be found on our Discord support channel (linked there).