Ruins...?

Sometimes ruins contain techs you already possess (particularly when they are ancient unique techs), so will give nothing when you colonize them.

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Unique tech numbers are seeded to static values at game start, presumably to guarantee that there are at least so many of each type on the map. Regular tech ruins just have a number of levels seeded, so should always result in getting new techs from colonization.

SpaceEmpires.net | Space Empires Wiki

As Fyron said, sometimes you will discover one of the ancient techs that you have already found with another ruin. Also, the ruins will sometimes give you the next level of one of the standard techs (Armor, Supply, etc) which you might not realize. Both of these should show up in your events record.

"We are the Vahl, resistance is...welcomed"

I just got a ruin in BM 111 v1.63 with nothing in it, I checked and double checked, zilch.

It does seem a bit disappointing when you are cake hunting, would be nice if it would boost research points in the field even if it doesnt give you a whole level, I suspect it was military science 2, which is very useful in the early game, but I already have that as it is too late in the game. I would be dead without it as it is the hardest settings team game (without intel) and half the AI are ahead of me in tech.