Many of these kind of issues are bacterial infections, accelerated by water conditions.
Either not enough water changes, not enough cleaning of filters, that result in producing high nitrate (20ppm or above) and sometimes water temps too warm.
Many normally benign bacteria become problematic at water temps at or above 82'F, especially for species like trimacs that come from Mexico (as far north as north of Acapulco) where water temps vary quite a bit day/night, seasonally, where rain fall in the mountains brings cooler waters down stream, and heavy winds reduce water temps.
I kept mine at temps in the mid 70s, with enough water changes to hold nitrate to 5ppm.
What is your water change schedule, amount changed, and filter cleaning routine?
What is your average water temp?