For those pissed (me included) with the lack of a proper, functioning Undo/Redo functionality in Ableton Live for the third party plugins, after reading some VST developer forums on the subject and lots of back and forth with Ableton's support, I'd like to share here a simple workaround. It is not a bug fix per say (yes, Ableton support guy confirmed that they know this is a bug), but it works and is easy to implement.
Background: I stumbled upon this comment from this old thread (https://www.kvraudio.com/forum/viewtopi ... o#p7648796):
After reading that I opened Live in Arrangement view and tried it: inserted a plugin, then changed some parameter and looked into the Automation options available. The parameter I just changed was available for automation, so I just hit Undo/CMD+Z and it worked!Some DAWs (such as Ableton and Reaper) are now supporting Undo for plugin parameters. I have discovered, however, that what gets recorded for Undo seems to be only the automatable parameters - not ALL parameters.
So how to "fix" that problem: add the line below to your Options.txt file:
-_PluginAutoPopulateThreshold=128
The maximum is 128, the default is 64 and 1 is minimum value. This will automatically populate all the Plugin parameters (max 128) to the device Configure Mode panel, making them instantly available for automation, which means whichever of those parameters you change will now be added to Live's Undo/Redo list. Voilà!
Now I know why the Undo/Redo used to always work for me, it's been several years I have that line in my Options.txt file and just recently I removed that because I thought having so many parameters was giving me more trouble to find the right one to automate. Well, that's the down side of having it
Some pictures:
https://imgur.com/a/LulMoqf
https://imgur.com/a/14ZukqM
Hope it helps
Luiz