Wacom Tablet not compatible with Roto Brush Tool?

My Intuos Pro M tablet does not function correctly when using the Roto Brush Tool. No matter what size I change it to, it still only registers a thin hairline, that will automatically select the entire composition no matter where I draw. I have attempted to change the pen pressure in my Wacom preferences, restart the computer, and try it on a fresh project with different footage - the issue remains. Drivers, firmware, and Adobe software are all up to date.

When using the Roto Brush tool with a mouse, I have no issues whatsoever, so it sounds like that there is either a software of firmware issue, but I am just wondering if anyone has found a workaround for this, or if it is just an existing bug / issue.

Thank you in advance for any information.

Intuos Pro M

Model #PTH-651

iMac, Late 2012

3.4 GHz Intel Core i7

32 GB 1600 MHz DDR3

NVIDIA GeForce GTX 680MX 2048MB

After Effects CC 2018 (latest version)