Are you parked in the same places when the fob stops working or does it happen anywhere?
There are three places, two in shopping center car parks, one on a main road where my fob won't work. Push the Jeep ten to twenty feet away and the fob works normally. Something in those areas is obviously interfering with the signal.
Long presses of the button work much more reliably than short presses for turning the immobiliser on or off.
If the the immobiliser looses sync (I think this has only happened after the Jeep battery has been disconnected for quite a while), the LED will light constantly. If it does that, I sit with the ignition on doing long presses of either button in turn, and the immobiliser always resyncs within a few minutes.
Aside from those issues I've found the immobiliser very reliable.
May and Schofield did have an option where they could add a touch key for the immobiliser but I have no idea if they could still do that and think the immobiliser had to be sent to them to add it.
Wranglerfix reprogramming to remove the M&S immobiliser the PCM is likely the best solution if you can't get the fob working.