I don't know what I specifically did other than change on of the transition animations and now they suddenly don't seem to work no matter what I do. I'm running Dopus 12 on Windows 10 Pro and they had been working perfectly fine up until now. I've restarted Dopus, Explorer, and Windows to no avail. The correctly display in the Prefs preview but not in any lister.
Are there any extra messages in the Preferences page for them?
Using Remote Desktop, or disabling animations system-wide?
None that I can see, it looks completely normal.
I am not using remote desktop and animations are fully enabled.
If you use File > Exit Directory Opus, then launch it again, do they come back?
Nope, already tried that thrice.
Does hovering over buttons on the taskbar show thumbnails of the windows there?
Yes, peeking still works.
I can't think of anything else, sorry. 
Thinking some more, the Prefs preview images work in the same way as the real animations, so if they are working then the real animations should at least work on the same monitor that Prefs is on.
If the window moves or resizes while the animation is playing, that will cancel it. So the only other thing I can think of is that something is resizing the window slightly when the animations play. But that would be quite unusual. (Could be done through a script, but I can't think why a script would do that.)
I'm not running any scripts, so I'm not sure either. If I attempt a reinstall, do I need to export my prefs/UI settings or will those remain?
Use Settings > Backup & Restore to create a config backup, and save it to a safe place.
If you uninstall and then re-install Opus, it'll remove and reset your settings.
After reinstalling, check if the animations are working first, and then use Settings > Backup & Restore again to load the backup you made earlier. (If one works but the other doesn't, that tells us it comes down to a setting somewhere.)
Weird, reinstalling didn't even reset the settings, so the animations still aren't working. Is there like a "factory reset" option of some kind?
EDIT: Whoa, while I was backup up the local/roaming settings to test this, the animations started working, but only in dual-pane mode. As soon as I go back to single, they stop.
Even weirder, single-pane animations work when DOpus is maximized, but not restored.
Uninstall, then re-install.
using multiple monitors with different scaling will stop transitions
That's exactly what I did.
All my monitors have the same resolution and scaling settings.
Is anything installed that changes how window frames look?
I've been using WindowBlinds, but it never seemed to cause issues before. I just tested switching back to default Windows and that restored the animations. Now I'm noticing an issue where in double-pane mode (restored) only the left pane uses animations.
Interestingly, loading the shadowless version of my WB theme completely fixed the issue. Couldn't imagine what the root issue is at this point.
That might mean the WB theme is inconsistent about the size of window borders that get reported via different methods of querying them. If a theme does that, the animations won’t happen. (May also depend on where the animation is in the window etc.)
Very strange, though I'm still confused as to why this wasn't happening before until now.
Whatever the case, I'll easily trade window shadows for the animations.