Zwift crashed while going for the 100 mile jersey, I did 102 miles, but it only gave me credit for 98 miles, then it crashed on discovery ride stage 5 when I was getting to the very top trying to get the Ven-Top badge. Dang Zwift!!! Crash on my easy rides not my hard ones!!! Part of the reason I do zwift is for the little rewards, it helps me train harder but it’s frustrating when I put that many hours towards something and end up with nothing! Rant over, time to get back on the bike.
Sorry to hear about that… Indeed, it happens (though not a lot, thanks, Zwift!), and is every bit as frustrating as you describe.
Possibly, you may want Zwift support have a look at the crash log, see Sending Crash Logs to Support
It happened to me before. But I found that ZWIFT capture the activities file as .fit file under your ZWIFT installation directory (ZWIFT->Activities).
You can upload this .fit file to the system to retrieve back your activities.