Rayman Legends

mine still shows 90% even though I have all of them

This didn't unlock for me either, despite having all 10.

Just got it to unlock, I cleared my series x cache and played a different game for awhile. I came back to Rayman and just decided to re-play the princess missions. I had been going between two xbox's. Obviously the save is synced to the cloud, however, when I re-completed the princess missions I had done on my other xbox, on my series x, the achievement unlocked. What was weird was on my series x, the achievement tracker was stuck at 90% and on travel xbox the tracker was stuck at 80%. If anyone is having an issue with this, and were playing between two xboxs, try doing all 10 princess missions on just one xbox.

I can confirm that clearing the cache resolved this issue... I also had to replay every level after clearing the cache, including those I had played on my current console.

For any other pool soul that got stuck with a glitch on this one - I replayed all the levels TWICE and didn’t get it to pop. I ended up popping it finally after getting the gold cup on the last one of the levels that didn’t have it. No idea why that would trigger it, but it did the trick for me!

Can also confirm clearing the cache worked but it might matter how you clear your cache. Clearing it by going into the Settings -> BluRay-> Clear Persistent Storage and then playing all the levels will not work, at least in my case. Clearing it by going into Network Settings-> Advanced-> Alternate Mac Address however will work. I even ended up only having to rescue 4 princesses instead of all 10 to get this to pop.

This glitched on me as well. I went back and forth on systems, got frustrating left it alone for about a year. Started it up, replayed all the save the princess levels and it popped.