I was able to finally fix this issue after many many hours of troubleshooting.
First step was buying a new IR Receiver which did not help.
I then triggered a “Factory Reset” from volumio.local and setup volumio from scratch.
After re-installing the IR Remote plugin, I was finally able to see pulse/space outputs using:
sudo mode2 -d /dev/lirc0
… but Volumio was still NOT responding to the remote.
Only after DL and installing a different version of the Apple A1156/lircd.conf (and restarting volumio/RPi) was I finally able to get the remote to work.
The version of the Apple A1156/lircd.conf which is shipped and installed with v 1.2.3 of the IR Remote plugin is different to the version that I DL:
lirc.sourceforge.net/remotes/apple/A1156
I am not sure if the shipped version works for any A1156 remotes, but it does not work for all.
Can I request that future updates of the IR Remote plugin offer support for 2 versions of the A1156/lircd.conf.
My remote (shipped with an early 2009 24" iMac) has the following markings on the back:
Model A1156 EMC 2086.
Also of note is that the process of replacing the A1156/lircd.conf is not forgiving.
For example, you cannot backup the existing A1156/lircd.conf into the same directory, as it causes subsequent errors in the IR Remote plugin interface.
The system also needs to be restarted after replacing the A1156/lircd.conf and selecting it in the UI.