If the bank allows a borrower to pay interest only on a past due loan upto 90 days in order to bring the loan current, are we required to have a signed deferral? - Upon receipt of interest only payment for the past due period, the bank will adjust the due date to bring the loan current.

I appreciate any help! Thank you!

I haven't seen this requirement. I'm in Texas and was at a national bank.

The reason you would want this though, is as a measure of control. You should have a policy and verification process so that you don't appear to be hiding past dues with extensions. You should monitor how many accounts get how many extensions, how often.