iPhone 13 mini not ringing

Why is my 13 mini not ringing when receiving calls? I've been waiting for a call from the vet today (dog is having surgery) and heard my voicemail alert, but the call didn't ring (or vibrate) in the first place. As I was just about to play the voicemail, they called again, and it rang through (and vibrated) normally. The first call isn't even on the call log, but the voice mail info from the first call has the same phone number as the successfully connected second call. Additionally, the voicemail alert sounded 17 - SEVENTEEN - minutes after the voicemail was recorded.

I had not changed any settings between the calls, and my phone was not even locked for either call.

• DND/silent mode were not activated
• The ringer volume was on high
• The phone was not connected to Bluetooth
• The caller is in my contacts list, and does not have a unique ringtone
• I don't have another device set up to receive calls
• I don't have call forwarding
• I have wifi calling enabled, and was connected to wifi for both calls (no problem with wifi, as the zoom meeting on my PC was not affected at the time the first call came in)
• My iOS is up to date

This is not the first time this has happened, and I have restarted my phone in the past (and again now) in an attempt to fix the issue.

Why are calls not ringing, why am I getting the voicemail alert so late after the message is recorded, and how do I fix both?

Thanks.