Today I’ve had my 4th ride which has malformed when trying to upload to Strava internet didn’t drop out either Zwift just froze, after doing all the usual things using fitfiletools none of which worked. Do Zwift actually have a support set up where they actually work through and repair these file for use on Strava etc. Starting to become frustrating now tbh
No, they wont fix fit files. They may work with your log file to determine what has happened. I’d send your log and details through via the web site support.zwift.com to see if you can address the root cause.
Mate I’ve sent the log files to all 4 rides I’ve ridden and still haven’t heard anything off any of them rides. Ive not known of a set up like this where there isnt any support or a simply way of recovering the ride, Ive not had this much crap since owning a Garmin head unit
Yeah I used the word may wisely as I am in the same position (wihich is why I help out here when I can)
Same boat as you with Garmin too – lesson learnt is never be a Garmin HU/watch early adopter - nothing but pain.
Wish I had more advice for you Lee other than try a different Zwift platform? Even if its temporary to help you isolate where the problem might be? Maybe if you have an iPhone/Android phone you could try instead?
What sort of setup are you running on? Is it a laptop with Intel integrated graphics? Tell us more about these freezes.
For the first time since I was a Beta Tester for zwift - game Froze on me today mid ride on the PC. 
Never had any other issues with zwift at all in all these years.
Bummer really… But hey ho… Still working on the Companion App fine, so I finished off n saved it via the App.
Just using iPad at the moment, maybe worth trying another method I don’t know