Freewheel engaging sporadically when turned backwards at low speed
There's a sprung pawl mechanism that is responsible for allowing the cassette to drive the wheel in one direction and coast in the other direction.
The problem you're having is indicative of something not right inside that mechanism. Possible examples are the pawls or springs being out of place, mangled, or not made to spec.
Freehubs not breaking in correctly is something that happens, and there's not much a user can do to either cause or prevent it. One path to issues occurring is if the lubrication inside is too thick, it can cause the pawls to not spring up fast enough, which can cause partial engagement, which can in turn cause damage. Once any of the parts are damaged, the problems escalate.
It's possible that if you were able to disassemble the freehub body completely, there might be a correctable problem. Actually doing that for a looseball cassette hub is seldom done and usually requires special tools. It's also finicky and on the advanced side. And, it's more likely that at this point something is damaged inside.
In my experience, when a freehub is giving the symptom you describe of taking force to break free and rotate in the coasting direction, something is destroyed inside and fixing it is impractical. There are many freehub problems that can be solved with lubrication or thinning out the existing lubrication, but this isn't one of them.
You should take it back to where you bought it for warranty help. The ideal solution is to put a new freehub body on it, which is a quick fix if one is available. Shops have an unfortunately hard time with having access to replacement freehub bodies for bikes they sell, so this is not always practical. From there the options are either new hub or new wheel, which likely won't be OEM graphics/color-matched. I would be accepting of either.
If getting it warrantied isn't an option, it probably makes the most sense to just go for a new wheel, or re-hubbing the existing rim if you want a project. Continuing to ride it is a recipe for it failing at an inopportune time.