How do I fix 'You left the conversation' issue in mixed group chats after upgrading to iPhone 17 Pro?

I upgraded to an iPhone 17 Pro recently and I have been running into a strange issue with iMessage in mixed group chats that include both iPhone and Android users.

Several times a day, these group threads suddenly display a system message that says “You left the conversation,” even though I never leave the group. I still receive all messages in the thread on my iPhone, and I can continue replying as normal. However, the message keeps repeating itself as if I am leaving over and over.

Here is an example screenshot of what I’m seeing.

The second part of the issue is on my Mac. In the Messages app on macOS, I can still see all the mixed-group messages, but I am not able to reply to them at all. The text field is present, but sending a message does nothing. It is like macOS believes I’ve actually left the group while the iPhone does not.

Troubleshooting I have tried so far:

• Turned iMessage off and back on

• Restarted the iPhone several times

• Confirmed I’m signed into the same Apple ID

• Verified phone number and email addresses for iMessage are active

• Deleted the message threads and started completely new ones

• Updated to the latest version of iOS 26

• Checked for carrier settings updates (none available)

None of these steps have fixed the problem. The “You left the conversation” message continues to appear repeatedly in any mixed SMS/MMS group, and macOS Messages remains unable to send replies even though the iPhone still works.

Device details:

• iPhone 17 Pro, iOS 26 (latest version 26.2)

• Mac running latest macOS Tahoe 26.1 (Messages syncs, but cannot send to mixed groups)

• Carrier: Verizon

• Issue only affects mixed iPhone/Android groups, not iMessage-only groups

Before the upgrade to the iPhone 17 Pro, I never experienced this behavior.

Has anyone else seen this after upgrading, and is there a known fix or setting I may be missing? Any guidance would be appreciated because it is becoming pretty disruptive and very annoying.

[Re-Titled by Moderator]

Original Title: Messages keeps saying I left mixed group chats I am still in and don’t intend to leave, after upgrading to iPhone 17 Pro.