I have the same ideas you mentioned:

1. Clear Cache (browser and nostr cache)

2. Don’t have many browser tabs open. Close all or nearly all.

3. Sometimes copy the nest address and put it in a freshly opened browser and paste the nest address into the newly opened browser.

My iphone browsers I use:

Safari

Brave

4. Turn your mic on in the nest.

5. Make sure your applications on your phone allow the mic and speakers.