Just had a thought, reverse is generally a lower"gear" (a numerically higher ratio) than any forward gear--that means for any given vehicle load less torque being transmitted through the CVT. That lower torque requirement could show itself if a jammed up movable pulley face in the torque multiplier is also present,
The spiral slots in the outer (movable) pulley hub are the Torque multiplier cams--the pins (p/n 5) are the cam followers)
The torque spring (p/n 3) forces the pulley faces together, working against transmitted torque to keep the driven pulley effective diameter large and the variator (drive pulley) working diameter smaller (I.e. a "lower gear)--this happens while the variator centrifugal weights are also trying to make the variator pulley effective diameter larger. This battle between the two is part of what determines the overall CVT ratio.
However when torque needed to accelerate the vehicle reaches a certain level the belt slips on the inner (fixed) driven pulley face but not on the movable face causing the outer pulley half to try rotate--if it can rotate the torque multiplier cam and its followers work with the spring to force the driven pulley faces further together to further increase its effective diameter (if not already closed completely) and thereby forcing the variator face apart decreasing its effective diameter--temporarily forcing a lower yet over all ratio until yet another equilibrium is struck. when vehicle torque demand falls off. This is why the assembly is called the "torque multiplier".
If the outer multiplier pulley was jammed on its shaft unable to rotate and effect pitch diameter , a lower torque demand (as in reverse gear) could cause the belt to effectively loosen, slip in both sheaves , and squeal.
110% speculation, but its been 8-9 months, what else do we have? And I would bet "dollars-to-donuts" it's a CVT issue.
Not sure I explained this fully or sufficiently clearly, if anyone has questions or comments let 'em fly...