Can't select multiple layers at once

This was working fine earlier yesterday, and then after my system updated (macOS Mojave) it changed and it’s driving me crazy: I can only select one layer at a time, even if I hold shift, which is workable but clumsy and but slowing me down considerably.
I checked to make sure it’s not just my computer, and I can confirm it’s only happening in SBP6.

Is anyone else having this problem, and is there a solution or do I just have to wait for the driver to catch up to the system update?