I thought perhaps Lucas might rough cut his version on the fly with the video dailies he was receiving. He and Coppola were keen on that sort of thing long before Hollywood got on board.
IIRC, some Wampa shots didn't work as planned, like the one of a claw breaking through an ice wall in the rebel base, and they gave up on it to keep things moving. That scene made it into the Marvel adaptation though.
If you've seen the SPFX documentary, the Wampa couldn't walk very well on location!