I am on Windows 11, using Animate CC 2019, and have the same issue! Unfortunately, Hawri's solution of changing the shortcut from Ctrl + tilda to Ctrl + 7 did not work for me. Holding Ctrl while clicking on "Smart Magnet Joint" inside the EDAPT Commands also did not work.
An additional bizarre observation: While Inverse Snap does nothing for most child symbols, for two specific child symbols that are parents themselves, Ctrl. + ` accomplished exactly what ` would have (snapping them onto their parents rather than inverse snapping their parents to them). This is not the case for other symbols that are both children and parents.
The exact same behavior happens when I tried this on the sample FK Robot: Ctrl + ` did not work for the most part, and when it worked for the robot arms, it did a normal snap.
I am perfectly content with with working with regular snap, and use 1 then move parents & children together to avoid the need for inverse snap. However, if there is every any development on the issue, I'd like to be notified!