Not because the other person deleted everything, but because iMessage decided you were fine as you were. Apple has finally admitted it: iOS 27 had three unpleasant bugs, and all of them got on your nerves.
The first was disappearing messages. You open a chat, the latest replies are there, but what was in the middle has evaporated. The cause turned out to be iCloud syncing: the data simply didn't load in time, and the system showed a gap. The second was messages not sending. You tap the arrow, but the send time never appears. The third was chats freezing: the keyboard won't open, the input field disappears for a couple of seconds, or the app crashes altogether.
Checking that everything is fine after the update is simple. First, go to Settings → General → Software Update and make sure you're on iOS 27. If you've already updated but still have doubts, ask someone to send you a message and restart the phone. Watch that when you open the chat the whole history is there: scroll up and find messages from two days ago. If they're there, syncing is alive.
After the update, Apple recommends giving iMessage time to finish downloading the data. An hour or two, and the whole history should catch up. If after that time the gaps are still there, old chats won't open or new messages won't go through, that's no longer a bug but its aftermath.
iMessage can be fixed in various ways: from signing out of the account and back in to a full reset of network settings. At the workshop we regularly see cases where, after conversations have collapsed, people rewrite everything important from scratch: the wording of agreements, addresses, details. Notes on paper by the keyboard are still a thing, but technology is meant to hold this for you. The main thing is to update and check, right now.