Thank you! I haven't tried this yet, but seeing this pop up as a new addon and knowing it exists at all means I wasn't going crazy before.

I was recently reviewing a couple of my characters and realized that some passives were gone from some important lines. It made me wonder how long I had "forgotten" about that, but now I know there's a good chance I didn't.

The what bug ? Was there a thread on the eso forums about this ? I haven't played for a while and have no clue.

Hint: If you want to speed up access to your self.SV.selectedEffects table, as it will be read quite often due to the combat/effect events, you should add a local pointer to that table in your addon code.

local selectedEffects = self.SV.selectedEffects

Do that outside the events, directly in your addon code, e.g. prepare local selectedEffects at the top of your addon and then update it with
local selectedEffects = self.SV.selectedEffects in your event_add_on_loaded after your SavedVariables got read.

And then use that local selectedEffects to update/read the SVs table directly.
Else each combat event will search table self (which btw is a bad wording... self should ONLY be used if you are using "classes" and create objects from it e.g. class ZO_Smithing, Object SMITHING = ZO_Smithing:New() -> self = pointer to object SMITHING. ou should simply instead use your table LostPassives or somehting like local lp = LostPassive instead of usng "self"!)
and then searches for subtable sv and then searches for subtable selectedEffects again and again.