I noticed this immediately because I use kanshi (highly recommended for laptops running sway!). I don’t know the how or why (maybe it’s the wlroots bump), but when I upgraded Sway to 1.9 today, the Hex ID form one of my external monitors changed. So I had to update it in the config for kanshi to work again.
Just a heads up for other kanshi users, and people whose scripts may be influenced by this.
FWIW, I just played a local mp4 video using VLC on Sway (1:1.9-1 from Arch repo), and this seems to have been fixed