R6 AF tracking issue.

Not sure if I can follow you.

I try to interpret it: You are not actually in "small area / single point" AF mode but in "tracking + detection" mode with initial servo AF point set to the single focus point. Then you want to start tracking by selecting your subject with the focus point and pressing bbf. Then the subject you want to track is not actually being tracked with the "single af point" you had as the inital point but it will often "decompose" into a dynamic cluster consisting of a lot much smaller AF points, this is what you call "matrix squirrley". Sometimes the single focus point will turn into a "small rectangle". Those points or this rectangle will not really be sticky but will "reshape" over time and sometimes will drift a bit around on your subject. Sometimes it will drift right at the start when initialising the tracking.

Did I get this correct or am I completely off?

If I am correct then the answer is: Yup, the Canons are not really good for "any object tracking". Canon has probably the worst implementation of this of any brand. Depending on the subject and subject features and other elements in direct vicinity "any object tracking" performance will be in the range from "really good" to "really bad".

The "workaround" or "canon way" of doing it is not relying on "any object tracking" for "select and recompose via tracking" but to actually move your focus point manually, e.g. by using the touch screen or with the joystick. This will yield better results, at least for somewhat static use cases. For more dynamic objects (where one objects moves independently in the scene) tracking seems to be more reliable. Best performance will be achieved by actually "detecting" the subject, which certainly does not work for most inanimate objects though.