Solved. I opened the port installer, uninstalled the driver and then reinstalled it.

I tried reinstalling the driver for the port but this did not make it appear. I am not sure what caused the port to "disappear" because for the better part of a day it was just there under Tools and uploads were working just fine. I am running OS 10.11.6 on a mid 2010 MacBook Pro. Tried shutting down the computer and starting up again, but this did not work.

How can I restore the port?

How can I ensure repeatable coded flights?

I am very particular about:
-no debris on propeller shafts
-propellers in as new condition
-current on all firmware and software and library
-still air indoor space
-fresh, fully charged battery inserted every time code is flown
-drone bumper is seated properly
-motors have seen relatively little use and seem to be fine, but probably need trim adjustment because even after running the calibration routine, some drones still drift

And what sort of accuracy does a coded flight have (given that no trim is needed)? Can I expect a drone to fly the same course over and over to within say +/- 250 mm or is that unrealistic?

How many minutes of flight time are motors good for, before needing replacement? I am thinking in terms of a preventive maintenance replacement schedule. A log of flights could be kept.,

Hello. I updated the firmware for a drone via the iPhone app and then performed the recalibration by popping out the battery, putting it back in, holding the reset button on the side of the body of the drone, waited for the light sequence, turned the drone right side up, placed it on the floor, it took off, but did not hover as expected. The drone continues to have a bias in drifting or rolling right. I also checked all the propellers for dust/hair by popping them off. The propellers look new. The bumper guard was seated properly and the motors seem to be fine.

I tried uploading the sketch that allows you to adjust the trim while flying a drone, but this code would not upload due to a coding error and I am not sure how to fix it. Help, please.

I suspect that unless a drone flies well using the controller manually, then it is not going to perform coded instructions reliably.