“Not gatekeeping in the problematic sense”

Problematic

Here means:

potentially unfair, biased, unjustified, discriminatory, or improperly exclusionary.

Sense

Here means:

the particular meaning or way in which we are using the term.

So:

“Not gatekeeping in the problematic sense”

means:

The filtering may technically be gatekeeping, but it isn't necessarily improper or unjustified gatekeeping.

For example:

A journal rejects a paper because its central evidence is fabricated.

That is a gatekeeping decision in the broad sense.

But it is not necessarily problematic.