blinking of satellite bars in rover u centre for rtk2board . I am using a BT module either in UART1 or UART2.

Blinking satellite bars can be because you have different NMEA and UBX messages trying to provide the same/similar information.
You could also be have an overload of data. If you see $GNTXT “txbuf alloc” messages you have too much data to push out of all your selected messages/interfaces. Cull things you don’t need.
Use UBX-MON-IO / COMMS / TXBUF to evaluate current situation