I can relate to a few similar experiences as a windows user, which are almost always asset-resource problems it seems.
I have some silly plugins (I think some old Softube stuff, I forget which), which absolutely crash unless I have a Soundtoys 'Effect Rack' loaded in the session first (it can be deactivated, but has to exist in order for the other plugins to load).
It's a silly thing to try but might work.
As for it working on the old version but not the update, try this:
Open your old S1 session where the plugin opens correctly, and note all the other plugins in the project. Try to have those same plugins present with at least one instance in the v6 project.
Or, simpler, just load various v5 songs in v6 where the Melda was working fine.
Does auto align load in any of those song projects?
If so, it is almost definitely the issue I describe before, with resources for the Melda plugin failing to load without having another plugin (of whatever kind you discover) open first.
Good luck!
