I just found out that 1.3.3 is where this is happening.
I'm guessing your on aseprite 1.3.3 that just updated a few days ago D:
It seems there is some major issues with transactions in 1.3.3, I've reached out directly to Aseprite this morning to see if there was an unnoted change.
TO FIX FOR NOW:
https://gyazo.com/3d09d01bd54afaa358e3c330e5d08d80
Simply revert to 1.3.2 like so and everything will work again!
Sorry about this! Sometimes things are out of my control and it's inside aseprite itself. I'll be digging deeper in to this if there is something I need to change for 1.3.3 but so far nothing on the docs says there was a change :(