Why do my up-side-down porch (yellow, incandescent) light bulbs seem to burn out but still work when I bring them inside and try them on a right-side-up fixture?
Have you looked into the socket to see if it is rusted-out or has lots of dirt/bugs in it? Upside-down outdoor sockets can get ‘weathered’ pretty quick, IME.
Maybe its the filament. If it has separated while upside down the two sides would tend to separate further. Putting it right-side up the two may fall together, allowing electricity to flow.
There’s also the possibility that the filament has broken somewhere but inverting the bulb causes a loose end of it to fall back into place connecting to the rest of the filament. If so, it should completely burn out shortly.
My guess would be that the upside-down fixtures are getting a bad connection somewhere.
just to be clear, which side of the lightbulb is the up-side and which side is the down-side?