Hello! I seem to be having the same issue as described above, where I am not able to receive an invitation to view my parent's health data. However, I am able to send an invitation to them, where they got an invitation right away. My iPhone is IOS 15.1.1, whereas my parent has 15.1. Both of us have two-factor authentication on, iCloud for the Health app on, and have each other's phone number and iCloud email on our contacts.
I looked all over for any troubleshooting recommendations, including the official Apple Health sharing instructions, as well as I did all your suggested steps of restarting my phone. Is this a glitch from an update, or am I missing something?
Any suggestions would be appreciated. Thanks.