I have seen this reported a few times, suggested options have been:
- Check the battery connections and make sure they are tight.
- Battery health check/replacement,
- DC/DC Converter replacement.
For the DC converter I also read somewhere corrosion on one of its connections can be part of the issue, I don’t know how viable it is to check and clean these.
I have seen DC converters online for much less than the official parts network will charge, however unknown history etc..
I haven’t heard of Mazda contributing to this however there is no harm in asking.