CarPlay not playing Siri audio through car speakers, and missing notifications

I have a 2025 Honda CR-V Hybrid touring with the "fancy" Bose speaker setup. My phone, running iOS 18, plays audio fine...but when using any Siri functions, the current audio source completely cuts out (usually Sirius on the infotainment system) and Siri speaks through only the speaker in the dash that's directly behind the infotainment screen. My husband's phone does the same thing in my CR-V, but both of our phones play Siri over his car speakers with quieted (not silenced) Sirius radio in his 2024 Ridgeline which has no speaker behind the screen. According to a conversation I had with them, Honda thinks this is an iOS issue with the way it takes over the existing audio source and doesn't play through all the speakers.

Also, both of our cars have ceased to get popup notifications of iMessages on other input source screens (Sirius, Bluetooth, FM radio) since iOS 18. We only get the popups if we're in the CarPlay screen.

We've been through the delete/forget and re-pair cycle several times, and I've even factory reset my infotainment system twice. I cannot get Siri to function as it should.

Anyone have this issue as well or found a way to fix it? Or am I stuck waiting for Apple to fix this bug?