Vast sweeping generalisation:
Being a trainer tends to steepen the authority gradient from the other pilots perspective. Most people will know that the perception of the gradient depends on the individual; you may think you are the most approachable guy in the history of aviation but that doesn't make it so. Being a trainer adds a 'he is probably right' percentage into the subconscious of the other guy that might just tip the scales away from being being challenged.
I've managed to screw up quite a lot of things over the years, but I think the only serious airborne error was an altitude bust; I miss set the altitude preselect. The F/O confirmed the setting. In the subsequent debrief he said that he had briefly thought that I might have been in error but discarded the possibility as I was much more experienced than him and had been one of his trainers. (He was only a few days past his final line check and really should have known better.... but such is life).
Whether this sort of CRM factor is statistically significant.... <shrug> who knows.
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pb