An achievement wasn't unlocked

Recently I've been playing Forza Horizon 3 and last Friday (September 16th) I decided to at least unlock one more achievement since I wasn't far away from unlocking it. The achievement was called "Who's Hiding These." I'd already smashed 137 boards, so I only needed 13 more. As I was curious, I've been checking the achievement progress from time to time while hunting the achievement and it was progressing normally. However, after smashing the last board, the achievement wasn't unlocked. I've also checked the achievement progress and it was stuck at 99%. Normally I'd check the troubleshooting guide and that's what I did. I'll quickly run down the steps recommended on this website: https://support.xbox.com/en-US/help/games-apps/achievements/troubleshoot-achievements-challenges
- making sure I was connected to the Xbox Network - there was no sudden halt in the Internet connection and the Internet was working well,
- checking the Xbox service status - checked and there was no notification regarding Forza Horizon 3,
- checking achievement progress on the console - checked both Forza Horizon 3 achievements section and the "all achievements" section and despite the around 72-hour wait the achievement still remains locked,
- checking achievement progress online - done that and still the achievement remains locked,
- restarting the console - done that and the achievement is still locked.
I've checked some posts on Xbox Forums and I'm fully aware that Microsoft cannot trigger achievement unlocking by themselves, but I'm looking for a possible solution of an issue. Unfortunately, I've already smashed 150 boards in this game, so if the only way of unlocking the achievement is to restart the game and to smash all those boards again, it wouldn't be ideal as it could take way over 10 hours to find and to smash 150 boards again.

:)