Out of sync playback - PC & 2 androids

Hello all,
I'm a bit of a newbie to this. I have searched but have not found any answer I can understand.

I have a
PC running Logitech Media Server (Audio out via USB) playback with SqueezePlay app
Android TV (Nvidia Shield) running Squeeze Player (Audio out via USB)
Android phone Note7 running Squeeze Player (minijack output)

Playback happens simultaneously, all are controlled via the LMServer but is never properly in sync. I have unsynced and resynced all the devices, in various orders, several times... but to no avail, it is still not working properly.

Sometimes the sync is as much as a second or two out, usually half a second or so. They are all out, it is not like any two of my 3 devices can be synced either, they are out of sync.

Is there something I am not doing that is causing this, or is this "normal"?

Thanks,
Mark.