KYB/Onboarding - As Prop Firms still have many problems with this?

I want to ask those who frequently trade with Prop Firms: are you still encountering many issues with KYC/KYB or onboarding these days? I've tried several, both small and large. Sometimes the information doesn't link up, and I have to resubmit documents. I don't know if the problem lies with the broker that the Prop Firm uses or the Prop Firm's own backend system. As for spreads and commissions, that's another story. Some claim to be cheap, but when trading, I frequently encounter slippage, which is frustrating and makes costs balloon. This doesn't even include withdrawals. Some are easy to withdraw from, but with others, it's almost a fight to get your money back. Does anyone have similar experiences or advice on what to focus on when choosing a Prop Firm regarding these infrastructure issues?