Side-chain compression is only active for a few seconds then it stops working.

I’m using the audio bus to send from a “Dialogue-MetaSound” to a side-chain compressor. The compressor ducks ambience when characters speak.

It works - but only for a few seconds. Then the ambience fades in again, even though the “Dialogue-MetaSound” is still active and emits sound and therefore sends to the bus.

Anyone else encountered the same problem?