Mojave 10.14 Mouse Hover Suddenly Not Working
Hover is something that comes out of the gesture recognition engine on macOS so it's more complicated than simply the cursor is now over a link. It matters if more than one finger (multitouch) is detected and it also needs a stable input.

One rare cause of this is flakey USB that causes a (possibly invisible) shake to the input - this is filtered out, so you might not see it.

The leading cause of this is when there are more than one device connected. For Macs with a trackpad, if there is motion detected on the build in trackpad, the external device may be demoted to &quot;secondary device&quot;


I learned this when the same issue plagued me for a few days. The cause and solution was similar as well - little did I know, the USB-C dock I had my Mac plugged into at work also had a USB mouse plugged into it, hidden behind the monitors. As soon as I unplugged that mouse, the issue immediately went away.
If anyone is having this issue, try seeing if there is a mouse or wireless mouse dongle plugged in that you might have forgotten about. Also, the act of disconnecting a USB device or Bluetooth device and re-connecting it (which is a different / quicker step than unpairing and pairing) that also seems to cure when a hover motion doesn't get detected.