Hi, as requested by Shayla over at Microsoft Support she has asked me to post this thread.
This will be a long story short post, I’ll try to keep it short 
4 days ago I signed into my friends gamertag so I could do some races for him, I did a bunch of races then he signed back in and we played some Forza, later on we did that again, though this time I could not sync his save, it popped up with the syncing data screen however it showed no progression bar and showed no percent.
So I contacted Microsoft support and spoke to someone named Lily, we tried trouble shooting for about an hour nothing worked at all, in the process of doing trouble shooting though, she had asked me to delete my own profile from my Xbox One so I could resync to see if it was just a problem with my friends gamertag or something else. Note, that I had never said I had an issue with my gamertag and I have never had an issue with it. So I delete my profile and redownloaded it, I synced all my games perfectly fine, they showed a progression bar and a percent except for Forza Horizon 2, it showed the syncing pop up but did not show a progression bar or percent. I have kept it syncing for a max of around 30 minutes, all my other games take less that 2 minutes to sync. So continue on, I tell her what has now happened so now I get asked to delete my saved data for Forza Horizon 2 from the Xbox One console. I do so and try resync nothing works. The last option she gave me was to reset my internet and if that doesn’t work to delete the game and all DLC and redownload it. So that night I reset my internet and deleted the game and all DLC and redownloaded, still nothing.
The next day, now 3 days ago I went back and spoke to Microsoft Support and spoke to Al B. I told him what had happened and he read through last nights chat log, we did more trouble shooting with no luck. So we then confirmed what really we already knew. The issue was with Forza Horizon 2 only, I can sync all other games fine and play them. We even had my friend try and sync my data on his own Xbox One it had the same issue that I get (he can sync his stuff fine he gets a progression bar and percent but not when he did mine.) In the end he gave me an email address to email Turn 10 about the issue, which I did instantly.
It’s now been 3 days and I have not received an email back yet, I spoke to Microsoft support again, I spoke to Shayla. She wanted to confirm things like, Do I have Xbox Live? Can I play other games online blah blah. So with nothing working she told me to post a thread here.
Let me add that, I love Forza and a pretty annoyed about this, I’ve played Forza since Forza 2, I played Forza Horizon 2 every day and my garage is worth about $30 million and have a little over 400 hours played. I really want my save back, can’t do anything without money in this game.
Edit - Shayla has given me an Xbox One avatar shirt for all my troubles.