1A3oTB6fV4WpVz6hR2m7NogX2Hsjq18nxr sends 0.25 BTC to 1AcquN6CvGP4hxb5pKtYG8K7wdiLbSdxBg (Bittrex address) and remaining change to 1PPGsDnHWprZXBpsYq7yAv5oaL7DtNePWD on 2018-08-21 [TXID].
Next day 1PPGsDnHWprZXBpsYq7yAv5oaL7DtNePWD sends 0.49 BTC to 1AcquN6CvGP4hxb5pKtYG8K7wdiLbSdxBg (Bittrex address) and remaining to change address [TXID]. I believe that the Bittrex address is personal deposit address of his account and 1A3oTB.. and 1PPGsD were part of same wallet.
Checking the deposits i.e incoming transactions to 1AcquN6CvGP4hxb5pKtYG8K7wdiLbSdxBg(Bittrex address), I found many frequent deposits being made from same wallet.
For instance, some transactions made from Wallet [02987ecd8a] to 1AcquN6CvGP4hxb5pKtYG8K7wdiLbSdxBg
My report is based on assumption that there is no option for a user to ask for a new deposit address in Bittrex.
Also considering the post gap from 2016 to 2018 and the fact that user used to post in Russian sections only but have discontinued posting on in those sections after the gap, it is likely that the account is hacked/bought in-between.