Strange output of Temperature probes
The drop in temperature during Sun AM establishes that the compressor works without producing pickup in your sensor, particularly if (as you indicate) the wires were not moved during the test, although the little glitch near the beginning of the trace may well be such pickup.

This pretty clearly indicates that the temperature swings you're seeing are real. The regularity of the swings, especially in amplitude, and to some degree in timing, also argue that the swings are real, and the freezer controller is doing something odd. The suggestion that this is a defrost cycle seems reasonable, except that I'd expect that more often, like once a day or something similar.