The bummer is that the only way to upload a FIT file to Zwift’s servers is by saving & uploading. If something like a WiFi flutter or a game crash interrupts that - then it won’t save properly.
Good news, though: for Tour de Zwift - there is a way to get credited, which you can read about on this other thread. Stage 3 is a beast, so yeah - I wouldn’t want to re-do that either.