Ring Doorbell 4 not recording - help!

Hi folks. Hoping someone on here can help. I’m having an issue with my Ring Doorbell 4. It’s set up with a motion zone, to record (but not alert) anything that moves across the field of vision of the camera. This includes the area covering the gate to our front garden. It does this fine, picking up and recording all movement of folks walking past our house on the street. However, it’s not recording anything when someone comes through our front gate and into our front garden, which is movement within the motion zone and directly in front of the line of sight of the camera. The recording on the doorbell obviously does kick in if the doorbell is rung, but if someone simply comes up to the front door without ringing the bell, it’s not recording. I’ve played around with the settings, increasing / decreasing sensitivity etc. Tried everything. It’s bizarre as folks coming into the front garden walk directly through the same motion zone that does record if someone walks past the house. Any advice gratefully received.