I am on Windows 10 using Audacity 2.3.3. I have a Roland Rubix 24, using it as both line in and audio out.
I have followed the steps at Tutorial - Multi-track Overdubbing
and can record my first track. I can play back this single track, and also hear whatever I play through my guitar on top of it.
When I try and record a second track as per the tutorial (Shift + R), I get a noticeable but faint click/tish sound then nothing (apart from a note in bottom left to confirm recording) - my original track doesn’t play, and whilst I can hear my guitar, I can’t see it being recorded.
I can click stop, after which I am able to click play - though it plays only my first track and there is nothing in the second.
It’s tricky because symptoms and causes vary from one machine to another. I’ve added a tip in the trouble shooting section:
If you are able to record a single track, but attempting to record a second track fails to record anything, or throws an error about sample rates, check in the system sound settings (for example, Windows “Sound” settings) that both the recording device and playback device are set to use the same sample rate as the Audacity project.
This update will appear in the next release version of the manual.