Firstly, I love the transparency on this topic and I love to see Monzo coming back to being open and honest about things! (It’s why I choose to support Monzo!)
This is a bit of a shame it feels a bit industry-blocking. It would be great if there was a better way for the target bank to be at least notified “there’s a payment soon” but that’s well beyond Monzo’s reach.
Maybe something like you can get a link like https://track.monzo.com/A33GT643F and it’ll say “£200 will arrive to you tomorrow pending checks” so at least there’s proof to a legitimate person that it’s on it’s way? Otherwise I can see this causing arguments of “well i did send x money” etc,
I’ll be honest - I find the temporary escrow thing a horrible idea - if a detailed chat with a fraud specialist that other banks use when they’ve blocked a suspicious payment can’t convince someone they’re being scammed then I doubt a few hours can
I can’t even imagine having to pay for something last minute and getting hit with hours or days of escrow blocks
as a sole trader who helps fairly non-it literate customers with their computer issues, my fear is that my business will be flagged up as “incredibly risky” and the messages will scare the customers in a way not quite intended. I’ve already had this from a customer trying to pay me online with barclays, warning messages were displayed, the transaction was blocked, their account temporarily frozen, and they had to write me a cheque! VERY frustrating to be on the other end of!!!
Out of interest, are you using an actual business bank account for your sole trader business, or just a standard current account?
Based on that experience, I’d expect the latter, and would guess you’d be less likely to run into such an issue with a proper business account. Part of the checking process involves whether the recipient is a personal or business account, and I’d be concerned and surprised if these measures are impacting folks trying to pay business bank accounts.
Did the customer chose they were paying into a business account though? Barclays gives you the option and often people chose the wrong one, I’d imagine the bank then bases their warning upon that
possibly not, despite me telling them, and I’ve added clear instructions on my invoice. but unfortunately a lot of people don’t look at the invoice carefully (if at all, apart from amount & account info) and non-it literate people struggle thru these sort of things generally. a lot of my customers I have known for years, but I know they would still be spooked by warning messages when paying me, they would think “something else” might be going on with the transaction. to be fair, having a bank they’ve never heard of doesnt help me - they like & trust the old traditional banks - the fools
will comply with this 
