Say the issue is call metadata. They showed that I called the murderer, who then murdered someone I had a grudge against. So this evidence doesn't prove that I did order a hit, but at least proves that I had the opportunity to have done so.

The metadata is technical evidence, not witness testimony. But...

Who wrote the software that collected the metadata? Any bugs in it? Any possibility that I did not, in fact, make that call?

Where was the metadata stored? Who had access to it? Could anybody have altered it, perhaps even to cover their own tracks?

Who had custody of the data after the records got pulled from the database? Any chance that they could have altered it? Maybe they knew that the prosecution's case was weak, and they wanted to make it look better?

In this way, technical evidence does in fact depend on witness testimony.

Does that happen in every case for every piece of technical evidence?

I think it has to. The only way it could not is if you had a piece of physical evidence, and you were going to extract the technical evidence from it there in the courtroom in front of the jury. But even then, you have to worry about the chain of custody of the physical evidence, and about the tool you're going to use to extract the technical evidence in the courtroom...

Perhaps it does but I'm not convinced without evidence it happens and I can't find any that shows it happens the majority of the time let alone all the time :/

Well, I think what happens in an actual court case is, you check out the chain of custody if you suspect that anything is actually fishy, or if you can make the prosecution's case look weak. If there's nothing there that you can use in your defense, then it never comes up in court.

Could be. But imo, anything the FBI touched would be suspect.