jekis, I am not sure what you were seeing or where so here are a couple of points of information which could be associated with a missing Title.
1) Rebuild Lists - (Series Information and List of Owned Series) can resolve some missing Titles. CB 2020 seems to rely on some 'static' lists. If new information is introduced (import, or just adding a New Title), a Title may not show up in Find results (or the suggestion list when typing in the Find box on the main screen). I may not be describing this 100% correctly but when I have not seen a Title that should be there, the Rebuild fixes it (mostly).
Fortunately, Rebuilding these two list is very fast so it doesn't hurt to try it out.
2) Using the View drop-down option Items to Show. You could set this to Owned Items and forget you set it. That could account for some Titles not being found.
I agree about CB 2020 using static lists; I ran the update last night and it removed a new title and issue I had created the day before - a task I'll now have to repeat in order to maintain the accuracy of my collection.