Possible cause

WARNING: This page is about a different car, the 2020 Mazda CX-30. However, it is still accessible from the selected car via links, so may be relevant.

Connector terminal disconnection, poor contact, damage, deformation, corrosion
Rear side radar sensor (RH) power supply voltage or body ground malfunction
Open circuit in wiring harness between rear side radar sensor (RH) and connector C-70
Open circuit in wiring harness between connector C-70 and connector C-58 (with parking sensor system)
Open circuit in wiring harness between connector C-70 and connector C-68 (without parking sensor system)
Open circuit in wiring harness between connector C-68 and connector C-69 (without parking sensor system)
Rear side radar sensor (RH) malfunction