not that it's user error, tests can be wonky sometimes, I'd test a fresh batch of known saltwater and see what the value is with your test kit.
if you test a 5g of newly made up redsea blue bucket saltwater and it's reading what the bucket says it's a good chance your test results are accurate, if so just add some alkalinity to bring up your tank value, then test again in 30 minutes to see if there is a change in your test results, no scientists needed lol
here's an easy calculator for adding alkalinity solutions to your tank.
Bulk Reef Supply - Saltwater Aquarium Supplies for Reef Tanks
www.bulkreefsupply.com