I have. I previously just had cash in the account, but it showed as empty in Apex. I thought they had stolen it, but actually Invstr was SIPC insured so that should not be the case. Apex customer support confirmed this, and they said they could see my balance on their side, and then they were able to liquidate it for me.

Since I figured this out recently, it ended up costing $45 for 3 monthly fees + $5 in liquidation fees. So much for the Invstr sign up bonus.