Stop putting culture centers everywhere, it's not at all useful.

Culture push is a decentralized force, and halves with each additional jump.  If you have two adjacent planets, and you put four centers on each with direct lanes to a single enemy planet with eight centers, you're toasted on both planets.

If you put eight on one, you're matching them from the one planet, and still in the same condition on the other.  You want to focus your culture production against theirs, not spread it out all over creation.  It should never be behind a front line planet being pushed unless it's an absolute necessity(someone stacked an adjacent desert with culture and you can't stop it with just your terran or take the planet), the most you want outside key points, is an individual center or two to spread it around your interior for the allegiance boost in a large empire.

If you're up against the Advent, they may have maxed out culture on their starbases, which gives them a decidedly overwhelming production level.  In a case like this where you simply can't match the flow, your solution is to base and build up a fleet at that location to take down their system.  Your capital ships will suppress their culture spread, keeping your planet safe in the meantime.  The solution is not to fill half your logistics with culture centers in a futile attempt to match the spread at small fractions of their original value.