Common issue in 1.1 patch. Previous thread.
Save your xp on the last slot point until you have a stats to put max stat into and have enough xp to buy them all. Gangers: 3 max on level 6-9,12 on level 10. Leader:6 on level 6-9, 15 on level 10. Suggest somewhere around 3000 xp to get leader from level 9 to 10. Neuro inhibitors help if you have infamy points.
Hoping lost max stats should be restored on next patch since the lost amount can be calculated, uncorroborated by developers though.
I'd expect recalculation at next level up when it would naturally add more points but then that wouldn't work for level 10 chars, probably would have to do something special there as all upgrade spots and skills could be maxed. Is a pretty simple calculation so doesn't seem unreasonable to check after each match I guess. Some ppl streaming also seem to be reporting they haven't seen any points replaced.
Edit: I've let 2 characters in an existing gang have unspent max stats and they haven't disappeared after 2 matches. Unspent points always went away for me previously (4 times I believe) after playing a match so it seems at least they aren't lost now.