I heard this a few times on a conference call recently.

Problem:
I do not know why two “net” adjectives are needed, and I suspect that many other people don’t know, either.

Explanation:
The speaker was explaining the effect of an action.

It has become popular in American English to say “net effect” instead of just “effect”.

I understand modifying the noun “effect” with the adjective “net”; it means something like final result.

I do not understand modifying the phrase “net effect” with yet another instance of the adjective “net”.

Given this lack of understanding — and I’m sure that I am not the only one — it doesn’t make sense to have two instances of the adjective “net” in a row, unless one is absolutely certain that everyone in the audience understands that distinction.

Solution:
“… net effect …”