Source: WowAce

With the latest version of the addon, opening the Awakened Caches upon completion of the machine awakening scenario is giving too much credit for attempts toward the mount. According to Wowhead, only a single object (https://www.wowhead.com/object=464938/awakened-cache) can drop the mount - this is the one for doing all 20 waves.

Instead, multiple opens of the different caches are counting toward mount progress. For an accurate count, this means manually going in and adjusting down the number of attempts.

Rarity doesn't actually use object IDs to detect game objects, but rather tooltip scanning (based on the object's localized name). Unfortunately, that means there's no way to differentiate between the caches by their ID. There was no wowhead data suggesting they'd need to be treated differently and the implementation is based on user reports, because I have no way to test the detection ingame (nor access to TWW content in general).

If there's a way to retrieve the object ID when opening containers, the detection can be improved. However, I'm not aware of one.

One vague idea I did have:

Since wowhead seems to be tracking what players received from opening the containers, and they use an addon (called "wowhead looter") for this, there should in theory be a way to figure out what they're doing and reproduce the relevant parts in Rarity.

This might warrant an investigation, although I don't think I'll have time to tackle this anytime soon. Maybe someone else will ;)