Click on the "Select Model Groups" button and see if you have any model groups selected. If you do, only models in those groups will be displayed. If none are selected, then the models with "Part of my display" are shown.
:lightbulb:
Finally sunk in. I've been struggling with the 'model groups' vs. 'part of my display' thing last year. I couldn't get some models to display, so actually had to make a model group for a single model in order for it to show up.
In essence, one must choose if the layout will be displayed based on the 'part of my display' checkbox when creating the model, OR create model groups, and if checked, they will appear in the layout.
Now knowing this, I deselected all the model groups. I can now delete all the model 'groups' that were not groups at all, but only single elements, like my star, sign, orb topper, megatree, etc. This caused me some confusion last year as I had models and model groups for star and sign named the same thing, so when I was adding them to the timeline in the sequencer I would see two items for star and sign, not knowing which was which.
Thanks Dan!