A lot of people experiencing the missing deposits and the support only gave auto-reply check FAQ thing.

https://bitcointalk.org/index.php?topic=2644751.0
https://www.reddit.com/r/Bitcoin/comments/7m16f0/bittrex_deposit_missing_cases/
https://www.reddit.com/r/Bittrex/comments/7m2llw/bittrex_deposit_missing_even_after_being/

so far I haven't heard anyone with 'solved' result.