Other option than backing out of the loadout screen
This works: swap out one of the weapons on the balky loadout screen with any other weapon in your inventory and then change your shield.
Then swap the weapon you want back in.
Note that the shield problem sometimes occurs with grenades also.
Trion acknowledged the bug with a patch that didn't fix the bug, so they know it exists. I figure they'll get it fixed about the time I get thoroughly frustrated with the bugs and broken mechanics and bored with the repetitive gameplay.