If it was simply isolated to the mouth, I'd venture to believe its simple lip locking scrapes.

But the white patches higher on the head, the patch in the dorsal visible at 14 secs, and on the flank at @45 secs, all look similar, and may suggest something more. Bacterial? Fungal? even viral?
What is the temp of the tank? mid 80s is perfect temp for cultivating bacteria.
What is the water change schedule, and amount.
I agree, being mostly vegetarian, any plants will be decimated.
Were they recently shipped? The stress of shipping often leads to viral infections like lymph (as in most viruses, no meds are useful, only clean water)
Was the cat added without quarentine, after the Uaru?
Was the cat the first fish? often old fish are immune to infections the new fish aren't, and present in the tank, if the Uaru were added later, an acclimation type quarantine.
Is your tap water hard? and highly alkaline?
Some soft water species become susceptible to infections in hard water, that are normally benign.
I'm guessing that's why the leaf litter, to add tannins.
I realize, not much help, but there could be multiple reasons, or just one.
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