Just an update… I pre-purchased the Shadowlands expansion and got the new mount. This mount did update the achievement count from 375 to 376 but the count on my alliance pally should be 378. For some reason the Honeybee Harvester and Snapback Scuttler are not being added to the achievement count.
I once again did load all 28 of my characters just to be sure. The wowhead list page is showing the total of usuable mount on my pally to be 378 and the Mount Journal Enhanced add-on is showing it at 378 on this character as well. I would add a screenshot but seems it is not permitted or even a link to the screenshot.
I even used my free 120 boost or this character (was 110) to see if that was possibly the problem. It wasn’t so that was a waste of a free boost 