What you current have is not supported.
IM version 12.6.4 reached EOS in October 2018.
Mixing IM 12.6.4 and 12.6.8 components is also not supported.
You will need to upgrade all of the IM components to 12.6.8 to be supported.
But as I noted version 12.6.8 will reach EOS in April 2019 so you should also be planning a further upgrade of all IM components to a 14.x release the latest as of now is 14.2 version.