I have been running Ubuntu 14.04 until I installed 18.04. On 14.04 I successfully created a udev rule that upon certain USB stick insertion it run a script AND the system used to auto-mount the stick (udev rules did not automount the stick).
But on 18.04 (and 16.04) when I insert the USB stick, the script successfully runs but the system will not auto-mount it. Please bear in mind that if I insert the stick on a different USB port (that is out of udev rule) then the system auto-mounts it.
Could it be that the udev inhibits the system somehow to auto-mount the usb stick? what has changed?