I have a Pentair DE filter. Since I last backwashed after a long time, now, everytime the filter pump is turned on, DE comes out in the pool return jets. This lasts for about 30 seconds and then it's clear water. Also, when I add DE, some comes back in the pool.

The filter is less than a year old. I checked the multiport valve, changed the gasket(just in case). It seems fine.

Any help is appreciated.