I have Widex hearing aids. While walking and streaming music from my iPhone the hearing aid furthest from my phone cuts in and out. I keep the iPhone in a hip holster and have tried both hips.

The Bluetooth wireless signal has a short wavelength. Your body can get in the way of it and disrupt the signal - Bluetooth doesn't wrap around objects like some longer wavelength radio signals can. A Widex trainer at a conference I attended last year suggested that if a person complains about intermittent audio when their phone is in their back pocket, we should suggest they move their phone to the front so the signal doesn't have to try to get through their body to get to the antenna of the hearing aid(s). Since that sounds like what's happening with you  - the audio is cutting out for the aid opposite of you phone hip - try bringing the holster to the front and somewhat center. If that solves the problem, wonderful, you've made physics work for you! If moving the phone so you're body isn't blocking the signal doesn't fix the intermittancy, there may be an issue with your phone's antenna or the controlling iOS software. You would need to contact Apple about that. If moving the phone does work but you can't exercise with your phone in the front because of leg movement or some other annoyance, there are DEX accessories that can be used to provide a more robust wireless signal between your phone and your hearing aids. Please see your provider if you feel these may help. I hope that simply moving the phone solves your issue. Thank you for asking!

I have heard this issue with a few people with made for iPhone hearing aids.  There was a recent update that gave people a new option that is supposed to stabilize the Bluetooth connection.  If that doesn't work there may be an issue with the antenna in the hearing aid itself.  If that is the case it would need to be sent in to Widex to be repaired.  Your best bet is to discuss the issue with you hearing care professional.

I have seen the same thing happen, make sure your phone is updated as well as any apps that pertain to the hearing instruments. Often times this will go away with updates from apple. If it keeps happening take them in to your hearing professional. They may need to send instruments back to manufacture to check out hearing instruments.