I could not get the panel off so I called a repair service. The repair tech said that he could not find anything wrong with the refrigerator, but suggested that he could replace the cold control/thermostat.

He did not want to give a warranty for his diagnosis. I could see the heating start defrosting. He was able to manually start a defrost cycle. He did not test any parts with a multi-meter. Will replacing the cold control, fix my problem? I can install this myself.

I explained to him that the refrigerator turns completely off like it is going into defrost mode, but stays off for longer than 30 minutes. It does this every few hours. Previously, the defrost cycle was two or three times per day.

I noticed after leaving the refrigerator off for five days and doing a thorough cleaning that the temperature on the fridge side fluctuated between 34 and 46 degrees within a few hours. On my old Frigidaire SxS, the fridge side stayed cold for three days until the back of the freezer panel filled with ice.
Thanks for your help. Pic below is freezer after 24 hours.

time to get out the hair dryer or heat gun.
A hair dryer is less likely to melt anything important, but is quicker and easier than waiting for it to thaw on its own.
A judicious use of a hairdryer to melt the ice and loosen things up, will get the back panel loose, and let you see what is what..
While you are in there be sure to check the defrost drain for stray pieces of corn peas , rice. I can't enve count the number of defrost problems I fixed with clearing the drain.
BTW do you own and know how to use an OHM meter?