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You say "one of my BT extenders", you don't say what type of extenders they are, e.g. wi-fi or powerline adapters.
How many extenders are you using and, if they are powerline converters, were they originally from the same or different sets and are both extenders connected to the same ring main and consumer unit? and plugged directly into the wall socket (spurs and extension leads tend to present a problem when using powerline converters)
