Z21 issue, What am I doing wrong?

[Twoshortplanks]

It will maybe be obvious from this post that I am not too good at electronics so hopefully the answer is quite simple.
Basically I have moved to Spain from Aberdeen and my old mate wired up the layout as I was and obviously still am useless at electrics.
When I reconnected everything up and plugged in my black Z21 I thought everything was running ok but it’s not because for some reason, no matter which loco I have on the app to control all the locos move even though they all have been programmed with different numbers.
I thought only the selected one should move if the others have been told to stop?
I changed some of the cv address’ just to check I wasn’t going mad and they still moved even though the Z21 had never previously ran a loco with that address just in case it was remembering them and I had failed to stop them.
Any ideas? Please be gentle!

[Bigmet]

You can edit the topic title, I'd suggest adding 'Z21 Problem' to it, to attract attention of those that know this system.

I have used nothing but Lenz since making the choice of which DCC system to use 18 years ago, and it doesn't create problems like that, so I haven't a clue!

[Ironduke]

page 43 of the manual describes how to set the system to factory defaults.
It sounds to me like the system is not outputing an even signal. When running the train(s) are you able to run in both directions?

[RAF96]

You haven’t by chance reprogrammed these locos to the same address accidentally.

[Twoshortplanks]

Thanks I have reset the box to factory settings and that has cured it.
Thanks for the replies, I’m sure I’ll be back with a few more daft questions soon!