This could just be me jumping to the worst conclusions, I’ve kept clown loaches with many fish and never saw this however.
A common issue in the polypterus community is that we can’t keep certain pleco and I’ve even had synodontis I’ve had to rehome because they eat the slime coat off the polypterus. I’m sure this happens in other fish groups, I’m just unaware. It’s very bad for fish to lose the slime coat I’m sure you’re aware of that, it’s been known to kill some polypterus. I’d keep an eye on it if I were you. If it’s infrequent I’m sure it’s no issue but if it’s stressing the fish out then be cautious.
Best,
Mason