i just had a prod about google and it seems there are some reports of this happening with cheap ebay LED bulb replacements. if you do buy more, buy different ones from a known good source, if it solves the problem you know what the problem was.
Yup I had that too. I dont know why they do it but cheapo ebay ones do that after a while. Although they are about 10x cheaper than better ones, so it would take you a few replacements to make up the price difference.
there was one suggesting it was due to them being designed to 12V rather than the alternator running voltage of 14.5V. thats just a stupid mistake