I had this exact same issue, and ultimately ended up troubleshooting the hell out of it after coming across a bunch of forum posts (like this one) without success.
Turned out that my (Logitech) keyboard was mapping the F8 / Print Screen key to Win + Shift + S (the default "Screen snip" action sends "Win + Shift + S"), causing the native snipping tool to always fire. I had to remap the key to "Screen capture" in the Logi+ Options utility, which then caused the key to work as expected.