I can usually tell when mortgage rates begin to drop because my phone starts ringing with former clients who are trying to refinance. Often, their loan broker wants them to supply assurances that, if the living trust owns the house, the trust gives the Trustee the power to mortgage the property and use the house as collateral so that the lender’s interest is secure. (That’s a lawyer way of saying that the lender wants to be certain that, if the mortgage isn’t paid, they can take the house.)
Sometimes the lender wants a letter from an attorney certifying certain things are true about the trust — usually that it is revocable, that is valid under California law, and the Trustee has certain powers including the power to borrow. Often, they want this letter right away because it’s holding up the deal.
The issue underlying all of this paperwork is that some (but not all) lenders are uncomfortable because something other than the individuals applying for the loan owns the property (the trust). Here’s an article that explains this in more depth from SF Gate.