I had around 40k coins, but i lost them all.. I did NOT buy something ,of course.
IDK what happened.
The only things i did were upgrading cards, raids and campaign fights , refresh the page and clear the cache.
Unfortunatly i dont know when exactly i lost the coins.
Edit: It seems to happen again: I had 15k coins and lost them all.. This time i did not refresh or clear the cache.