tl;dr: The thing you must do to get the Prepared Spells Combat Mode to work properly is to fill in the number of spells that you're allowed to prepare in the Power Group - Spells pop-up box.
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Long time no post. I'm not trying to create a web presence for myself, I just post stuff when I think it might help others.
One of the things I love about Fantasy Grounds is how on the Actions tab, when you go into Combat Mode all of your spellcaster's non-prepared spells disappear so you can focus on the spells you do have prepared. This is not particularly useful for Bards and Arcane Tricksters who can only change out a spell or two per level, but is incredibly useful for Wizards, Druids, Clerics, and other casters who can change their prepared spells each long rest.
A couple of weeks ago, I was playing with a Cleric who was not getting this functionality, and I talked him through the process *very slowly* and still wasn't getting it to work -- that happens sometimes, and I made the wrong inference that this particular player wasn't good at listening to instructions.
Today I was experiencing the same difficulty on one of *my* clerics -- and all of the things I told the other cleric wasn't working. So I spent quite a bit of time fiddling with stuff and discovered how to fix it. Detailed instructions follow:
1) Click on the magnifying glass for one of your spells dividers (it can be cantrips or Level 3, whatever). The Power Group - Spells pop-up will appear.
2) In the power group, enter the number of spells you are allowed to prepare in the "Prepared" box.
3) Enjoy combat free of the distraction of all the spells that you *can* prepare but didn't prepare today.
