Gas and Oil Home Heating Furnaces - RUUD gas furnace intermittent shut-off

I have a RUUD UGPH 06EAUER gas furnace in the rental property I purchased two years ago. It isn't a particularly old unit and I do not know who installed it or when, as the property was purchased from an older person with dementia. This problem I have is a recurring problem since purchase. The unit, after working for a period of several hours, stops working, no heat no fan, and, after a period of several hours, will start working and heating again. I have had several technicians look at it and last year in mid-January, I changed the thermostat and the problem did not happen again for the remainder of the winter (which is not long here in Houston, TX). I thought the problem was solved but it started again this winter, mid-January. Last week the unit would not come back on and we discovered the limit switch needed to be reset for the unit to come on. We thought perhaps the air circulation wasn't good, the return air was smaller than what you see on a conventional unit that size, so we enlarged the return air. Two days later, the unit stopped again and it repeated its pattern of behavior, runs for a couple of days, shuts off for several hours and then mysteriously starts working again. My HVAC tech is as baffled as me but he thinks perhaps the combustion/draft inducer motor is going out as he thinks it is nosier than it should be. Does anyone have any other ideas? Thanks for your help.

the limit switch needed to be reset for the unit to come on

Perhaps you meant to say flame roll-out switch? Limit switches are usually self re-setting. Roll-out switches are nearly always of the manual reset type.
While a flame roll-out switch can go bad, I would be more concerned that an actual flame roll-out condition may exist.

Cracked heat exchangers and bad draft inducer motors are the most likely causes for the switch tripping.