Not in the industry, just someone who has gone through financing and refinancing a few times.

In most cases as long as you can back trace from account A to B to C you are fine, it’s when you suddenly deposit 30k and have no proof of where it came from that you can have issues.

In my experience for non-jumbo mortgages they have only gone back 2 months of bank statements, but only needed to be able to qualify/source the $ I was using for the down payment. So if I had enough to cover that in traceable transactions a large cash deposit that is unable to be traced didn’t have any impact. Additionally, if I had the time to wait, then once that cash sits there for 2 months it’s considered “seasoned” and would then be considered usable. I’m not sure if this would change if a significant portion of transactions was all cash or otherwise difficult to trace since in my case there were just 1-2 transactions at the time that were disqualified.