Evohome boiler control bdr91 comms issue

Hi I’m having intermittent comms issue with the bdr 91 controlling the boiler, rf check gives signal of 5 and it’s located in boiler cupboard 0.5m from the boiler, the problem I think is due to the builder using foil backed plasterboard and the entire bathroom and boiler cupboard in it is lined with the stuff, in fact all the walls and ceiling of the house are lined with it.

Everything else works great, the boiler seems to work and fire ok but has the slow flash red light after a couple of days, nothing in the fault log either for this.

Anyone my ideas?