I find that all my messages related to a group of our family members have suddenly only appeared on my MAC.

Hi tresun,

Thank you for participating in the Apple Support Communities. We understand you're not receiving a group message on your iPhone, but you do receive it on your Mac. This article has some steps that may help: If you can't send or receive messages on your iPhone or iPad - Apple Support.

"If you receive messages on one device but not the other

If you have an iPhone and another iOS or iPadOS device, like an iPad, your iMessage settings might be set to receive and start messages from your Apple ID instead of your phone number. To check if your phone number is set to send and receive messages, go to Settings > Messages, and tap Send & Receive.

If you don't see your phone number, you can link your iPhone number to your Apple ID so you can send and receive iMessages from your phone number. You can also set up Text Message Forwarding so you can send and receive MMS and SMS messages on all of your Apple devices.

If you have issues with a group message

If you’re in a group message and stop receiving messages, check to see if you left the conversation. Open Messages and tap the group message. If you see a message that says you left the conversation, then either you left the conversation or you were removed from the group message. You can rejoin a group message only if someone in the group adds you.

To start a new group message:

1. Open Messages and tap the Compose button .
2. Enter the phone numbers or email addresses of your contacts.
3. Type your message, then tap the Send button .

If you have other issues with a group message, you might need to delete the conversation and start a new one. To delete a group message:

1. Open Messages and find the conversation that you want to delete.
2. Swipe left over the conversation.
3. Tap Delete.

In iOS 16, iPadOS 16.1, and later, you can recover a message if you deleted it within the last 30 to 40 days.

If you still need help

• Try to restart your iPhone or iPad.
• Check your network connection. To send a message as iMessage or MMS, you need a cellular data or Wi-Fi connection. To send an SMS message, you need cellular network connection. If you turn on Wi-Fi Calling, you can send SMS messages over Wi-Fi.
• Check with your carrier to see if the type of message you’re trying to send, like MMS or SMS, is supported.
• If you’re trying to send group MMS messages on an iPhone, go to Settings > Messages and turn on MMS Messaging. If you don't see an option to turn on MMS Messaging or Group Messaging on your iPhone, then your carrier might not support this feature.
• Make sure that your device has enough space to receive images and videos.
• Make sure that you entered the correct phone number or email address for the contact."

We hope this helps.

Take care.