I updated both my USG-3P and UAP-AC-Pro to the latest firmware (188.8.131.5240612 and 184.108.40.20636, respectively).
In the software UniFi SDN Controller (MacOS) v. 5.9.29, under the Settings > Maintenance > Firmware section it shows this:
In the Devices section, the Controller shows this:
I have verified the firmware versions through SSH to the USG and UAP to be the same as in the Devices section.
Have I discovered a bug?