There are a few potential causes here.
1) Your run may not have been scanned yet.
Our Crawlers are continually scouring for newly completed Mythic Keystone runs. However, this is certainly not an instantaneous process, so if you have just recently completed a run you will need to first wait for Blizzard to show your run on your armory page (usually takes about 30 minutes to an hour), and then wait for our crawlers to detect the new run.
2) Your run may not be your highest scoring run.
By default, your character profile page shows only your highest scoring runs for each dungeon. However, you can click an individual dungeon from the table to see all of your recorded runs for that dungeon:
3) Your run may be attached to an old character
If you recently renamed or transferred it's possible that the run got attached to an old instance of your character. If you can look at other members from the run and see it there, then you can open a support ticket on RaiderIO and let us know so we can try to link them back to your proper profile. In the ticket, please provide both character names (if they are different) and both the old and new server so that we can get this fixed for you as quickly as possible.
You can find steps to help this process go smoothly here.