Android
Unarchive a Conversation in Google Messages auf Android
Google Messages archives a conversation instead of deleting it whenever you swipe it away or tap Archive from the conversation menu. Archived threads still receive new messages, but they stay hidden from the main conversation list until you move them back manually.
This is why a chat can seem gone even though nothing was removed. The archive keeps every message, attachment and read status intact, so unarchiving restores the thread exactly as it was.
How to unarchive a conversation
Open Tap on Messages ➔ Tap on Google Account ➔ Tap on Archived. This shows every conversation currently stored in the archive.
Find the thread you need, then Tap and hold a Conversation to select it. A small action bar appears above the list.
Tap Tap on Unarchive to move the conversation back to your main inbox. It reappears in the regular conversation list right away, in its normal position based on the latest message timestamp.
If a thread is not in the archive, check whether it was blocked or deleted instead, since both actions remove it from this list permanently.