I found that my minecarts ran away and throught they went into a wall or something at 2-3 points. The Track is about 100 Tracks or more in Size, and the the minecrats glitched out merging to compress then Decompress to go Extreamly fast.
They were 40-60 Blocks off the Track and went through like their was a Track.
I got so upset i lost 14 Diamonds and a Diamond Pick.
I was going to Creative to get it all back cause i also lost a chest full of Cobble which i needed to complete a building.
I had used X-Ray mod after the events have pasted on a Server.
When i found them they went right through a 1x2 Room.
Like it was Butter or their was a longer track.
Yeah i creative to get them all up again but i had a hard time with keeping them up due to Compression and Tight corners.

Where they came from? Up from Surface to bedrock.

How i found them? X-Ray mod, Only way without knowing what happened to them.