For XML imports, I routinely delete all explicit clefs immediately. I also re-assign each instrument so that the associated “instrument properties” is properly recognized (dynamics above/below, notes out of range, etc.). I also select the entire score and remove any overrides which may have imported as well: Reset Position, Reset Appearance, Reset Beaming, and Remove Forced Stems to get everything back to Dorico defaults [my settings] before doing any more editing. Things just seem to go better if I do so. 