I sent some amount of DERO coins (April, 4th) to my address what I use on this exchange. After some time they blocked DERO coin "very hard technical update" (as they said). After some time they open me a new address for DERO, but there is no my coins on it. I can not access to my "old" address.
I opened a support ticket (enclose all infos about my address, transaction hash and exact time), waiting for almost 2 months, and they said "We do not have Your coins!!!".
I hope that they will bring me back my coins...and that this is only a accident.
Waiting again for their support, i believe less than 2 months for answer.
from your description it looks like they may lost control of some private keys, and as a result access to coins on the affected addresses.