First of all, thanks for all your responses. Been stacked since posting the above. You are all indeed right. Mine seemed to have an app software issue as I rang a Gauge Master technician and he had the same fault on their unit. This was near the beginning of June.
I have only managed to get back into the loft now and check everything. Firstly the stop/go/lightning bolt issues seems to be fine. But I have another issue which I cannot seem to work out.
The blue light is constantly on and all seems fine, except as soon as I place a chipped loco on the track it moves straight away with all lights on an an an usual buzzing sound. I still cannot control the loco on the on selecting it on the iPad. To add to this, the loco won't stop when you press the stop button, but will if you stop the power to the track. I have checked there are no shorts and taken all other locos off the track. I have also just wired up two 1 meter lengths and tried it on there on both main track and programming mode, but it's still the same, the loco starts moving straight away with no control at all. I have tried different chipped locos and also non chipped (very briefly, and they do exactly the same.
I have also done the infamous 'turn it of and on again' on the app, the router and the Z21.
Press send with out asking if anyone had any ideas .