casino asking source of funds after i finally hit, never cared when i was losing

Dropped a decent win on slots last week and now suddenly the casino's all over me for source of funds stuff. Never once asked about it when I was playing all the time and losing more than I should’ve. Now they're holding the withdrawal until I cough up documents. It’s just annoying how quick they are to freeze your cashout, but they’ll take your deposits instantly for months without a word.

Anyone else run into this? I'm all for playing by the rules, but would be nice if they were consistent and upfront about what to expect.