PF2 - NPC's character sheet shows "Building NPC..." and stays there

I'm using PF2, and I've got the Bestiary package.  I'm set as GM for the campaign I'm working on.  I got the Leopard from the compendium, dragged it onto my map, and then went to the journal tab, and clicked on the character it had created, then switched to the Character Sheet tab - I've tried leaving this screen alone for several minutes to see if it would complete, but it still says "Building NPC..."  I've tried this on a different character from the compendium - a wolf, and I get the same result.  When I create a new character, open the character sheet, and switch it to NPC mode, that looks fine.  I also tried an NPC I had created weeks ago (also a compendium download - specifically the Dryad), and that one works properly. I have tried exiting the campaign and re-entering, and opening the NPC again, I also tried exiting Firefox entirely and then tried rebooting my computer, in case it was some sort of thing stuck in memory, but these monsters still seem to be failing to generate a character sheet.

Hello Mathias G., Please carefully work through to the first three steps of our guide to Solving Technical Issues : Step 1: Make sure to use the right browser. Please check if these issues persist when using both Chrome and Firefox. Step 2: Ensure that there are no extensions/addons interfering with Roll20. Please disable all add-ons/extensions. Step 3: Clear your cache If none of the above succeeds, please have your player thoroughly work through Step 4. (Don't forget the complete Console Log!) If you need additional information on how to capture a console log we have additional information here: Submitting a Console Log in Firefox Submitting a Console Log in Chrome Thank you!

Be sure that your character sheets are not popped out into their own window. You turn off this setting in Game Settings (the cog icon in the right-hand pane). Many Roll20 features do not work when popped out into separate browser windows.

Rabulias, thanks - I had to delete the journal entries I had created and get fresh copies, but now that they're not popped out into separate pages they're working.  Then, once I had loaded each one once and gotten the character sheet set up properly, I could turn the pop-outs back on, and they worked properly.