I haven't come across this since I posted here, so maybe it's been resolved. I'll update this if I come across it again.
I found the save.
Before landing, I had the interceptors tail the UFO until it landed (I don't know if that is an intended mechanic).
After landing, this is the save file immediately after it lands.
Hopefully this gets you the data that you need to fix it.
BEFORE LANDING.json
AFTER LANDING.json