It looks like I posted a few minutes too soon. By searching for osx mouse troubleshooting, I found this link on Daniweb on the first page of results, where JustOneThing said:

What fixed this problem (for me) was merely disconnecting the reciever of the mouse (a Logitech MX Laser ) and connecting it again. Oddly enough it wasn't sufficient to disconnect and reconnect the USB hub the reciever was connected to (as I initially tried out of pure laziness). I hope this is of assistance to someone :-)

Indeed I am using a Logitech MX mouse, and simply unplugging the mouse from USB and reconnecting it fixed the issue. That is not at all the kind of fix I would have expected.

The main thing I searched before, which did not give relevant results, was primarily 'osx cursor not changing'.

It looks like I posted a few minutes too soon. By searching for osx mouse troubleshooting, I found this link on Daniweb on the first page of results, where JustOneThing said:

What fixed this problem (for me) was merely disconnecting the reciever of the mouse (a Logitech MX Laser <some-number>) and connecting it again. Oddly enough it wasn't sufficient to disconnect and reconnect the USB hub the reciever was connected to (as I initially tried out of pure laziness). I hope this is of assistance to someone :-)

Indeed I am using a Logitech MX mouse, and simply unplugging the mouse from USB and reconnecting it fixed the issue. That is not at all the kind of fix I would have expected.

The main thing I searched before, which did not give relevant results, was primarily 'osx cursor not changing'.