At some point recently (not sure when, but I just notice it now when I opened up a program I had set to auto-open a mirrored window with triggers that runs functions to move and resize it), window resize functions (whether automatically through triggers or manually with hotkeys) no longer work on borderless Mirror Windows. It seems to still work on ones with borders, though.
I'm currently on Windows 10 Pro with Version 10.0 (Beta 13) of DisplayFusion.

I have two trigger rules. One to create the Mirror Window, and then another to move and resize the created window. Resizing sudden stopped working on borderless Mirror Windows even when trying to apply it manually (but the repositioning function still works), so I don't think it has anything to do with the trigger rules specifically. If I change the trigger rule to create a bordered Mirror Window, instead, then the resizing happens as expected.

Well, looks like borderless mirror windows can now be resized by Functions, again. But whatever was done to fix this now made it so all of my Trigger rules to auto-generate the mirror window, as well as the Trigger to move and resize the mirror window when it gets created, no longer work.

It's pretty weird that my Trigger settings that worked prior doesn't work now. I changed the rules a bit multiple times to see if I could get it working (but failed), but I made sure to change them back to what they were originally.

Actually, I just realized that ALL of my Triggers aren't working since upgrading to Beta 14.