I’ve been checking my Halo Waypoint profile for MCC PC and my highest skill rank on the page has not moved from 6. It is currently 11 in Halo 3 Hardcore.
Give it a bit of time, seeing as we just got a major update to the Ranked system practically a week ago. I’m sure they know about this issue.
The game history is also completely messed up, games are missing and some are out of order.
Can confirm the same happening to me; TS H3 is stuck at 1, while i have rank 13.
I have the same issue too, it’s sort of irritating, but in H3 Ranked I’m currently Rank 15, but instead I’m stuck at 2
Anyone had any luck with this? Most of mine are stuck at 2, 
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> The game history is also completely messed up, games are missing and some are out of order.
Halo Waypoint doesn’t have recent game info for Halo MCC matches unfortunately. When it comes to your rank, give it some time to update.
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> Anyone had any luck with this? Most of mine are stuck at 2,
Negative. Been stuck for awhile now as well.