Skoda Yeti Rear Window Heating Problem

The symptoms you describe, combined with the error code, strongly suggest a power supply issue. A weak battery can cause all sorts of seemingly unrelated electrical gremlins in modern vehicles. Before diving into the rear defroster wiring itself, have you load tested the battery? What voltage are you seeing at the terminals with the engine off, and while cranking?

I haven't load tested it specifically. Multimeter reading showed 12.1V engine off, and dropped to 10.5V during cranking. Is that drop excessive enough to cause the window heater malfunction, and also affect the windshield heating?

10.5V during cranking is definitely low. While technically it might still start the engine, it's putting a strain on the electrical system and can absolutely cause the problems you're seeing with the window heater and windshield. The control modules for those systems are sensitive to voltage drops. I'd strongly advise getting the battery properly tested, and likely replacing it. Given the symptoms and the readings you've provided, a new battery will probably resolve the heating issue. If a new battery doesn't fix it, then further diagnostics are needed, but my money is on the battery. Take it to a workshop for testing and professional replacement.

Took the Yeti to the shop as you suggested. Battery was heavily discharged and borderline defective. They replaced it and cleared the error memory. Rear window heater, and windshield heating, are now functioning correctly. Total cost 290€. Thanks for the assist.