I read something once and can’t remember where or produce supporting facts, but I read an article about a bloke having similar problem as you.
He was advised to use a quality 95 or 98 fuel (Shell, BP, Caltex) in his boat and to stay away from 91 and E10 being sold at cheap servo’s.
Can’t recall the reason why, but I can remember that the bloke changed his fuel and had no further problems.
Sorry I can’t produce supporting facts, just relaying something I read.