A more recent example: I lost $20 or $30 in Bittrex due to them blatantly disregarding their own rules of allowing non-KYC withdrawals up to a certain amount. Unlike Cryptsy they're still alive. To me it's a clear-cut violation of a written contract. I don't know if I can put a red flag on them though.
As much as I hated them asking KYC, I do recall receiving warnings about lowering withdrawal limits. Then after a while, they suddenly reduced it to 0 until I sent them an angry looking selfie.
How long have your issues with Poloniex (with your 10 XMR) lasted? Recent months (after Circle-take-over), their supports have been fast
I received a response in 8 hours yesterday.