Andrew:
Recalling this thread, here's something I read in a Honeywell remote thermo-hygrometer sensor (wireless) owner's manual:
"TRANSMISSION COLLISION
Signals from other household devices such as wireless
doorbells, home security systems, and entry control may
interfere with this product or cause temporary reception
interruption. This is normal and will not affect the
general performance of the product. The transmission
and reception of the temperature readings will resume
once the interference subsides"
It's clear that the 433 Mhz frequency is used by so many other instruments, appliances and household accessories that any one of them could cause that transmission collision.
Were you ever able to find the item causing your issues?
I myself had a great deal of trial-and-error setup with my sensors.
I have a super-insulated dwelling, with foil faced polyisocyanurate sheets between the sheathing and fiberglass batt insulation, also with a foil faced vapor barrier.
Plenty of RF shielding!
Took quite some time for me to locate my console until the line-of-sight through windows became dependable.
Henry