Obviously, something is awry. Changed filter media about 3 weeks ago, apparently something was dislodged. If I were to leave the pump on 24/7 it wouldn't be a problem as no media (Zeolite) blows back into pool except for when pump is stopped, then started. I held a strainer over a return when starting pump and media comes out for about 30seconds when pump is started, then diminishes to nothing during normal operation. Not a lot, but enough to know something is not right.
*Sigh*...really not look forward to emptying filter again to check laterals. Possibly multiport valve/spider gasket issue? That's easier to deal with. Or I'm wondering if there may be a 'pocket' around a lateral 'hinge' that allows it to move a bit when filter drains down/is restarted, allowing an small opening for media to pass into standpipe momentarily. Media also visible in sight glass during backwashing.
Unfortunately I really can't think of any way for media to get into standpipe aside from the lateral area.