That does look like a pretty serious bacterial infection. NFG is my go-to ABX (especially with butterflies):
https://store.nationalfishpharm.com/...ofuracin-green
However, many times a bacterial infection is "secondary" to a preexisting parasitic or worm infestation. So, a few questions:
1. What copper level was maintained? (Should have been 0.5 mg/L for 4 weeks with Cupramine.)
2. Did you dose Prazipro a second time, 5-7 days after the first?
3. Were these fish ever treated with metronidazole for brook & uronema?