I am not sure about 7.6.x, don't have that running at the moment. But in 7.7.2 you can use the Enable proxy control event to override use (and max. header length) of HTTP/2. Since you're able to use any criteria in a rule where you use that event, you can do it just for problematic sites, combination of site/user-agent or globally.
maybe it is not wrong to consider upgrading to latest version 188.8.131.52 since there are several HTTP2 bugs/issues already fixed in 7.7.2.x.
Here you will find a summary of the release notes:
Since I am not sure if this article is always kept up to date, you can also have a look here:
I know how to configure HTTP/2 under 7.7. Unfortunately, we will have to work under 7.6 for at least another 6 months.
So the question how can I enable HTTP/2 under 7.6? In the Release Notes, several bug fixes are used to indicate the presence of the option.
This is just wrong information in the release notes. There is no support of HTTP2 in 7.6.
I also checked the bug ID and there is only information for 7.7.1 and 7.7.2. I will check this with the documentation team and get this PDF updated.
I submitted this as a documentation bug a while ago I believe. (I think I sent it to Jon directly to pass on actually). Looked like it just got tagged on by mistake with the related 7.7.x release at the time.
I have forwarded this change directly to the documentation team. McAfee normally does not edit release notes of existing versions, but will handle this change this time.