There's a long standing iMessage bug which likely affects only a small amount of people but it completely breaks iMessage conversations for me in certain situations which I'll try to describe below. It's still present in iOS 26.2 and has been for at least two years (when I first noticed it).

The specific setup(s) when it breaks:

1. two SIMs active, iMessage enabled only for email addresses (no phone numbers enabled for iMessage), new conversations start from an email address. This setup works fine when using iMessage through normal means (via the messages app, start new conversation or reply to a new conversation). If the 'share' menu is used (eg: share a photo, share a wallet pass, anything share really) - when I select the recipient and touch 'send', iMessage completely breaks for that recipient with a message: "Cannot send message - iMessage needs to be enabled to send this message". The only way to recover that conversation is to ask (via other means) the recipient to send a message back and that will kick it back into gear. It will continue to work with the condition of never using the share menu. Note: if only one SIM is active, this behaviour doesn't happen, iMessage sharing works fine.

2. two SIMs active, iMessage enabled for email addresses but also for a phone number. New conversations start from an email address. This particular one is interesting. I start a new conversation and recipient sees the new message from the email address, as expected. Conversation continues as normal until I (you guessed it) - try to share something. If I do that, the message goes through but the recipient receives a new conversation - from the phone number I have enabled. Now, the recipient has two conversations with me, one from the phone number and one from the email address. I only have one and irrespective of where the recipient replies, I have only one. To fix this the recipient must delete all conversations with me (from deleted items as well) and start fresh.

It's easily reproducible using these specific steps (must use two active SIMs) - with only one SIM it works fine and there are no issues.

I tried reporting this bug via the apple report a problem website but I doubt it reached anyone that can actually do anything about it. If anyone has any way of getting in touch with an Apple Engineer (or similar) I would appreciate it. Thank you.