KYB/Onboarding - Do Prop Firms Still Have Many Issues 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'm not sure 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 issue. Some claim to be cheap, but when actually trading, I encounter slippage so often that it's frustrating, causing costs to continuously balloon. This doesn't even include withdrawal issues. Some firms make withdrawals easy, but with others, it's almost a battle 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 aspects?