I had the debris event several times - but as Barb has been saying they are random. I had the "vial" events quite often too - I found if I left my PDA alone for a while, and off, when I turned it on and returned to the game I usually had SOME event waiting for me. I think it depended on how far into the game and how long I left it alone though. The random events are just that, random! Best of luck getting the debris event! If you're trying to make a master builder with that there is always the option of starting over instead of waiting and hoping, and planning out how to have a master builder around at the end. Or, in future updates, they are planning to have an area/way to train builders at all times.
Again, good luck!
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Rebecca
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