Can I Believe These Oil Temps?

It is highly unlikely that your oil temperature dropped 40 degrees in 9 seconds. Could the thermostat be doing something odd to cause this to happen? I m not familiar with how they are plumbed in to the system.

The plumbing for the thermostat is fairly straightforward. If the temp is less than 180F it bypasses 90 percent of the flow around the cooler.  Above that and it directs more to the cooler.  If it's working...

I've attached a screenshot showing the first 40 minutes.  Takes forever to get up to 120F and then it wavers all over the place, including below 120F.  Very unhappy with this.

If it were me I would hook up a couple of thermocouples to a dual-channel thermocouple meter. You can buy them cheaply on Amazon or eBay, and make sure the probe wires are long enough to reach the engine from the cockpit. Use high-temperature tape or cable ties to attach them to various locations in the oil circuit. I would probably start with the connections to the oil cooler or the thermostat to see what is happening.

You may have to do several flights with the probes in different locations to form a picture of the situation. If you can get a meter that logs the values then that would be good as you could synchronise the time with your EMS.

How do I do that if the oil is in hoses or the engine?  The only exposed location is the cooler itself and that will no doubt be colder than the oil.

You can just strap the tip of the probes to the metal part of the pipes where they go into the rubber hoses. You would probably get a relative indication of the temperature of the oil even if you attach the probes to the outside of the rubber hoses. You only want a clue as to what temperatures you have at different points in the circuit.