If an overlapping sender and proximity receiver are initially disabled, but then immediately enabled using an animation, the receiver will report 0 until it is removed and then reintroduced to the sender.
This bug used to exist for all receivers on load, and was supposedly "fixed" previously, but still persists in this more limited case.
This bug is very easy to accidentally trigger, as if the sender and receiver are within a normally-off toggle, and the toggle is turned on, changing your avatar's scale causes the issue.