Ring Doorbell 2 doesn't always alert or ring Chime

I have the Ring Doorbell 2 running on batteries. I also have the Chime plugged in to the mains. Most of the time, if someone rings the doorbell, I get an alert on the phone and the chime sounds. However, everynow and again it doesn't. The doorbell will ring but nothing comes through to my phone and the chime doesn't sound. Its not a persistent problem and its not something I can replicate. It seems like it loses connection every now and again. At first I thought it could be the wireless strenght but I have recently upgraded my WiFi to a mesh network which has vastly improved my wireless range and strength. The RSSI of the doorbell is around 50 and the chime is around 42. Can anyone help? Thanks Marc