Reddit reviews Whirlpool 819043 Heat Probe, white

Water should flow out of hole pretty quickly,you could have debris in drain. Assuming fresh food section isn't freezing, consider adding heater extension to keep drain from freezing. https://www.amazon.com/Whirlpool-819043-Heat-Probe/dp/B00DM8JPZS

i noticed in your first photo that little piece of copper wire. my guess is that you have that wrapped around your defrost heater.

you can try putting one of these defrost probes in there instead. I always run some 1/4" tubing all the way through also and make sure it pokes out both sides, just to clear our any extra gunk.