Missing Cursor a login / startup

I don't know that it is a bug, but here are a couple of links:

OS X- Login window partially appears, cursor movement redraws screen

The following is not mine. I found it doing a Google search.

I had the same issue with my 2008 iMac and Apple support walked me through the fix yesterday...

1. Shut the computer down by holding the power button for 10 seconds

2. Restart the computer and press shift at the same time until you see the progress bar start moving

3. Once you reach the point where your screen goes dark and you see the cursor, type the first letter of the username for your computer, then hit Enter, then type your password, then hit Enter.

4. After a moment, you should see the spinning beach ball

5. Your screen should then move on to something along the lines of "Completing OSX Installation" (I can't remember the exact wording). Let it finish. After that it should go to your normal desktop and the issue should be fixed. (If your screen goes pitch black during this process, hit the space bar. I thought it wasn't working, but the screen was just sleeping).

Apparently it's an issue with an automatic update that never quite got past the login screen.

A Troubleshooting Protocol to Identify Problems or Fix macOS El Capitan or Later

You should try each, one at a time, then test to see if the problem is fixed before going on to the next.

Be sure to backup your files before proceeding if possible.

1. Shutdown the computer, wait 30 seconds, restart the computer.
2. Disconnect all third-party peripherals and remove any support software like drivers and plug-ins.
3. Resetting your Mac’s PRAM and NVRAM
4. Reset the System Management Controller (SMC)
5. Start the computer in Safe Mode, then restart normally. This is slower than a standard startup.
6. Repair the disk by booting from the Recovery HD. Immediately after the chime hold down the Command and R keys until the Utility Menu appears. Choose Disk Utility and click on the Continue button. Select the indented (usually, Macintosh HD) volume entry from the side list. Click on the First Aid button in the toolbar. Wait for the Done button to appear. Quit Disk Utility and return to the Utility Menu. Restart the computer from the Apple Menu.
7. Create a New User Account Open Users & Groups preferences. Click on the lock icon and enter your Admin password when prompted. On the left under Current User click on the Add [+] button under Login Options. Setup a new Admin user account. Upon completion log out of your current account then log into the new account. If your problems cease, then consider switching to the new account and transferring your files to it - Transferring files from one User Account to another.
8. Download and install the OS X El Capitan 10.11.6 Combo Update or 10.12.6 Combo Update or Download macOS High Sierra 10.13.3 Combo Update as needed.
9. Reinstall OS X by booting from the Recovery HD using the Command and R keys. When the Utility Menu appears select Reinstall OS X then click on the Continue button.
10. Erase and Install OS X Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

1. Select Disk Utility from the Utility Menu and click on Continue button.
2. When Disk Utility loads select the drive (out-dented entry) from the Device list.
3. Click on the Erase icon in Disk Utility's toolbar. A panel will drop down.
4. Set the Format type to Mac OS Extended (Journaled.)
5. Click on the Apply button, then wait for the Done button to activate and click on it.
6. Quit Disk Utility and return to the Utility Menu.
7. Select Reinstall OS X and click on the Continue button.

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Goodness, it worked!. I used the first suggestion from user Kappy (the easy one). In my case, after entering the first character of my user name, and then entering my password (all in the blind), I did not get a spinning ball. Assuming I did it wrong, I restarted and, surprise, I had a cursor and could bring up the password entry box. My system is a 2012 Mac Pro, with lots of add-ons, Sierra 10.12.6. For the past year I have been using the cmd-option-f5 route to get into accessibility so as to enter my password. Reboot was the only time I had the cursor problem.