I have had repeated iPhone connectivity issues with my Philips hearing aids purchased through Costco. This occurred prior to the latest iOS update and both pre and post the firmware update to the Philips hearing aids.
In addition to what you’ve experienced with one or both hearing aids indicating not connected to the control app on the iPhone, I repeatedly have streaming issues and issues with phone conversations where one hearing aid disconnects. With music streaming, often both hearing aids cut in and out intermittently. I’ve given up wearing my hearing aids on my exercise walks and have gone back to my AirPods due to this. It’s disappointing, but I’m done with trying to resolve it. Whether it’s and Apple issue or a Philips issue, bottom line, they don’t work well when paired to the iPhone.