crypto casino says my ltc deposit came from flagged wallet but its just my own coinbase withdraw.

Anyone else had a crypto casino claim your LTC deposit came from a "flagged wallet"? I literally just moved it straight from my own account on a big exchange. Same way I always do, never had a problem until now. They froze my deposit and said I need to prove the source is "legit," but I'm not exactly sure what else I can show them. I can screenshot the withdrawal, but it's not like I can prove much more than that. Feels like they're stalling or just don't want to pay.

I'm not huge on slots bonuses, but I've noticed lately that a bunch of sites are getting real picky about deposits and withdrawals. Is this a new anti-money-laundering thing, or are they just finding excuses? If I used a different exchange or tried another coin, would it make any difference? Anyone actually got their funds back after this kind of thing, or should I just write it off?