I wear Phonak CI processors. It's not just you. I've also experienced the volume drop on a few sites and apps. The Amazon iOS app does this. Each time I leave the app, ambient audio returns to normal.
It'd be interesting to see what a lawyer specializing in disability law would think of that.
At least in the US, I could see that being something that the ADA prohibits.
They’re kindly turning down the background noise so you can focus on shopping and buying more stuff.