Reefer guys

'15 SB210 Thermoking

I've got a yellow K, but no alarms. I've done this a long time and never seen this on this trailer or otherwise. Trailer set at 34, ambient is 75.

Reefer starts/runs and cooling fine. Battery good, voltage/alternator good. Oil level good.

Can't clear the K because there's no alarms to clear.

Went back to White T on its own for about 10 minutes then back to yellow K.

Any ideas?