Possible cause

WARNING: This page is about a different car, the 2017 Mazda 3. However, it is still accessible from the selected car via links, so may be relevant.

Connector terminal disconnection, poor contact, damage, deformation, corrosion
DC-DC converter (i-ELOOP) power supply voltage or body ground malfunction
Open circuit in wiring harness between DC-DC converter (i-ELOOP) and connector C-05
Open circuit in wiring harness between connector C-05 and connector C-32
Connector C-05 malfunction
Connector C-32 malfunction
DC-DC converter (i-ELOOP) malfunction