You can send feedback here where one of the options is to Report a Problem. This will be reviewed and if it is determined to be a bug in the OS, then you can expect a fix in an update.
Feedback - HomePod - Apple
If you prefer immediate support, then you can contact Apple here. For a bug in the OS, it is likely that they are already aware of it. Don't be surprised if the agent is not able to specify a release date of a fix or even confirm if it has been identified as a bug. Also it can be repetitive as they will likely have you do the same steps you have already done, like the factory reset, but that is the process they have to go through. The goal is to get to the end of the process where all the steps have been followed and without a resolution then a Support Ticket may be opened or a callback scheduled by an Engineer for follow up.
Contact Apple Support - Apple Support