Purchase a new pressure gauge.
Make sure hoses are attached properly, mine weren't and that presented a problem with filtering and backwash flows as well as "gunk" returning to the pool from the return.
Service your multiport: with the power off & unplugged unscrew the screws & open it up. Look at your spider gasket make sure it is attached properly; if it is ~ clean and lube it. Lube the center spring that works the handle. If the spider gasket is "ratty" (unattached in places/ chunks of it missing), replace it. *Put everything back together tightening the screws evenly ~ not too much pressure ~ you want it evenly distributed between the screws.
Open the tank: make sure sand is at proper level (I believe most recommend 2/3's full, but consult your manual)/ introduce a garden hose to the sand bed to free up any channeled sand. Close filter back up and go through a rinse cycle to seat the sand properly.
I would try the above before removing the sand and checking laterals. Double-checking connections / replacing the gauge / servicing the multiport and deep cleaning sand bed might be all it takes to get things working correctly. If you remove the sand & check the laterals, but have problems in the other areas you'll still have issues. So I would do the easier exercises first & see if that fixes issues prior to removing the sand, just because removing the sand is a buggar.
*edit for typos