I suggest you put your query to BT, the provider of the app/equipment giving you these issues.
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Without knowing all the detail, make sure you have DHCP turned off on the BT mesh system
Also, make sure the Master BT disc is connected to the Now Router. We've got Now working with BT mesh and its so much better than Now WiFi which is a shambles due to the fact their routers try to look like Sky set-top-boxes and point the WiFi to the roof (not into the room/house)