I just found out about this plugin, and went ahead to test it on UbuntuStudio 20.04.3 LTS and
Ardour 6.9.0 DAW.
Single instance of Vital 1.5.5 works perfectly. However, when i use more than one, after a while closing and reopening the plugin windows, the GUI starts bugging out on the new instances, it is flashing, and not all elements are drawn. only few random widgets seem to be visible and updating, and I have to restart the DAW and the plugin instances to get them working again for a while.
Sound is not affected, it is playing fine, and the presets are correctly loaded per instance, just the GUI bug so far.