I didn't read the other post, but it may be due to their property taxes and insurance price going up, which is happens and is inevitable.

Or it could be they got an adjustable rate mortgage while rates were crazy low and now that rates have come back up, their interest rate is rising. This doesn't happen with fixed rate mortgages, but the adjustable ones tend to have a lower initial rate and people just hope they will be in a position to refinance if the adjustable rate gets out of hand, though that depends on several factors and may involve paying several thousand in fees.