I opened a very old session (2018) and Ardour tells me that ZynAddSubFX was not found (and replaced it with the “dummy” place holder). It is probably because it is an older version of it, perhaps installed in a different way, since I do have it installed.
I would like to keep the settings from the old plugin, as I don’t remember how I obtained that particular patch. Is it possible to somehow make Ardour replace the old version of it with the new one (keeping the same settings of the old)?
Ardour stores the plugin settings in a subfolder to the plugins one, but I don’t know if there is an easy way to translate the .ttl file into a Zyn patch file.
I’m presuming the main problem comes from your session being made using Zyn v2 and that you now have v3 installed.
What OS are you using?
If it’s Windows then you could perhaps find and install v2 and see if that works.
If it’s Linux and you’re comfortable with compiling stuff then maybe try that route.
In the Linux case you could presumably trick your session into loading v3 but using the settings from v2.
I’m guessing it’s the lv2:appliesTo line in the manifest.ttl that tells Ardour which plugin to load, so if you edit that file and line to say whatever Zyn v3 announces (you can get that info by adding Zyn v3 into a new session and check the resulting manifest.ttl), and then make the same edits in the corresponding state.ttl file there is a chance you can get it to work.