On an iPad I have found this. I can hide the nearby rider list by tapping the list and quickly swiping to the right. There is no need to open the menu bar. If I tap slightly to the left of the rider list it will open the menu bar as well but continuing to swipe right over the rider list will hide it.
However, when swiping left, it is impossible to restore the nearby rider list as any time you tap in the area where the rider list should be it will open the menu bar and the swipe to the left will be read as changing your selection in the newly opened menu bar.
It appears to be that the tap selection area for the menu bar has been increased and is above (and by above I mean overlaid) the tap selection area for the nearby rider list thus making it impossible to access.
To restore the nearby rider list I need to first open the menu bar and then select one of the options that has an extended selection (ie, pace partner teleport, the change view (eye icon) or the emotes). Because these popup an extended menu and left and right swiping doesn’t work on these extended menus Zwift can now read the left swipe on the hidden nearby rider list to restore it.