Try spaying some Electrical Contact cleaner on the sd card terminals and immediately quickly inserting and ejecting it repeatedly. Do that a few times because it may be only that the internal contacts of the card reader are a bit dirty. You could spray a little into the reader opening itself before inserting/ejecting repeatedly but if you try that do not power up the unit until absolutely certain the cleaner has evaporated. Most dedicated cleaners are non-conductive but i'd be extremely cautious with it regardless. Use only genuine contact cleaner not anything like WD40 nor any other hydrocarbon liquids.
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