Hi Dave,
Thanks for the reply.
Yes, I have installed the latest version of play memories mobile on my Z5 Premium and also the latest firmware on my QX10.
Uninstalling and reinstalling of play memories mobile also done but still the problem persist.
I also have tried to use the QX10 with Airplane mode turned on on my Z5P to reduce interference (as some thread suggest that the lag might arise from interference eg: other WiFi nearby), but still the same result.
Thanks & regards,
Kay