Updated how ?
If you updated from the command line then you need to run
sudo apt-get update; sudo apt-get dist-upgrade once to update to the latest version of OSMC for Jessie, then run both commands again to complete the upgrade to Stretch.
This is because it is a two stage process - the first stage among other things updates your /etc/apt/sources.list to point to stretch so you will not be on stretch until you complete the second dist-upgrade.
It is not recommended to manually upgrade directly from an old version of OSMC to stretch by editing /etc/apt/sources.list yourself, because there are a number of fixes that had to go into place first (including changes to udisks and udisks-glue packages) before the stretch migration to make sure everything goes smoothly, hence the two step process.
Users updating via My OSMC will have both steps performed automatically one after the other.
The version of Kodi in our stretch repo is later than the last version in our Jessie repo, so if you did upgrade incompletely via command line I would just go ahead and run apt-get update and apt-get dist-upgrade again to complete the upgrade and then see if you still have a problem with Kodi afterwards.