Problem with Hue App on Network

[Tsingtao]

Hi having a really strange issue with my Hue App....

1) Off network using mobile data by Hue App will connect to my bridge and control lights fine

2) Alexa can use the Hue Briidge to control lights from on network

3) Using the app on the local network I can see the bridge is connected but the home screen never presents

Any ideas what is causing this one, it works fine using my previous ASUS router but pulled that out due to Broadband connection dropping. Could probably switch back but would be good to work out why - thinking a port used by the App on network maybe?