I have been using genuine k-cups for years and have on occasion found the lid separating from the cup. Recently, it has been happening much more frequently. Usually the lid separates about half way through the brew cycle. The bottom and top needles are always clean. I too believe this to be the result of an inferior seal.
As recommended by others, I purchased some thin foam sheets ( about 1/8” thick) from the dollar store and cut out a donut shape (large hole in the middle) slightly larger than the top diameter of the k-cup. I place the donut shaped piece of foam over the top of the k-cup when closing the top. This seems to apply enough pressure in most cases to keep the top of the k-cup from opening. The idea being to apply a little more pressure to the top of the cup.
This makes it a little more bothersome to make a cup of coffee, but I get to keep using my Keurig.