Battery doorbell communications lag

Doorbell to phone has a 5 second delay so it is not possible to hold a proper conversation with someone at the door. Is there a reason for this I can remedy or is it a fault with the doorbell?
Also the volume at the doorbell is very low making it very poor for anyone trying to talk to me.
I have uninstalled and reinstalled the doorbell but still the same problem.

I will say I do not own one but I would think it is linked to your router. So I wonder if you have an older router. I know the one I had was causing me issues staying connected.