Well that'll teach me to big up the Fit File Repair Tool as an option. My ride today came out as 0m elevation in RITMO (OK on Garmin and Strava) but no matter what I try today's ride stays at 0m !
Just Google Fit File Repair Tool for info on what it can do. It's saved my sanity a few times when my Garmins been playing up, always seems to happen on long rides doesn't it, and I could go in and remove the corrupted records and at least get something. Pricey though - about £30 I think.
I think I may kick RITMO in to touch. I like the idea behind it, but hey, I don't need it to tell me I'm getting slower :-(