I had the same problem and narrowed this problem down the K1 relay by measuring
the relay outputs for K1 and K3.
I decided to replace the K1 relay and have had no issues ever since.
Replacing a relay was quite an undertaking because I had to somehow
desolder 8 pins simultaneously. After trying out various methods without
success (removing solder with desolder braid, etc.) I created a U shaped
'heat transfer' device out of 1 mm copper wire and re-added solder
to connect the 8 pins with the 'heat transfer' device. Holding the
soldering iron to the 'heat transfer' device then allowed me to slowly
remove the old relay. Then I cleaned up the through holes with desolderbraid and installed the new relay.