Yello.
We are experiencing the same problem, except on PC (Steam). It would seem if anyone gets DNF/DSQ or disconnects in league race, it refuses to submit results and save - usually reverting back to an ongoing race or even qualifying (seems like revert to Qualifying happens if nobody made it to Q3, but we simply do not have the time or will to verify). Normally you can see the game communicating for 2-10 seconds and then going forward, but in this case it is immediate, ie the game likely not even attempting to submit, and everyone gets the same error.
Also, this very same issue was in F1 2019 after the update that added saving between sessions. Back then we gave up after ~30 hours of failed leagues, never having made it past Australia again because someone always retired or had a game crash (crashes being less common). As this is getting a little ridiculous, hopping on here in hopes for action. Anyway:
0. I may have answered some things in wrong order below.
1. Above
2. PC/Steam, Win10
3. Latest on July 19th right after the real life race, do not have access right now to check version number.
4. League (Private, on-demand, no voting)
5. Four attempts in 2020, but due to the same issue in 2019 it would be closer to 4 + 15. Varied game settings attempted, but below are those that were always the same I believe:
Full Practice, Full Qualifying, 50% race.
2020 (or 2019 in 2019) car performance (NOT equal)
Full damage
No ghosting
20 participants, AI included in points
6. Drivers older and up to date tested, firewall on and off tested, different host computer, different host account, different connection, game on SSD, game on SSHD, game on HDD, DX11 and DX12, probably among other things I can't think of right now.
Off-topic but kind of linked: Why can't we save LAN championships? Wouldn't this be a great option B for situations like this, since then we wouldn't be relying on any external connections or servers. This besides 2p Co-op Career and/or Co-op My Team would be the dream for me.