From a business perspective genuinely curious to know general location and bank name for this. In WA state I've only dealt with minor scrutiny (from credit union not bank) asking if the business is involved with cannabis otherwise it's been easy.
But they were specifically worried about the transfers being scams -- at least, that's what they said. They insisted on calling my other bank to verify that I was in fact the owner of the other business account. And I know there's been a big increase in things like fake real-estate scams, so paranoia is understandable.
However, the way bank fraud/risk departments work is generally completely opaque. I've previously had Bank of America refuse to open an account, with no reason given and no possible recourse. And I can't imagine a much more vanilla, boring, good-credit person than me, so I have no idea what set them off!