After updating to Virtualbox 6.0, everything seemed to be fine. After saving and restoring a VM, the shared folders would not always restore with it. Trying to manually re-mount them would give an error about no such directory. They would work again after restarting the VM, but they would randomly stop working again after saving and restoring a VM.
Today, I can't get shared folders to work at all. I restarted the VM, but the shared folders won't auto mount or mount manually. I downgraded back to 5.22, and even with the 6.0 guest additions still installed, shared folders are working again. I checked the log file and didn't see any errors.