Teams Chat messages disappears

You have already repaired, reset and reinstalled Teams and removed its cache, so repeating those steps is unlikely to produce useful new evidence. More importantly, Microsoft's current guidance says not to clear the cache for missing chats or channels because it does not resolve that scenario and removes diagnostic information. Reproduce the disappearing chat list once, note the exact time, and collect Teams support files immediately using Ctrl+Alt+Shift+1 on Windows. Compare the same account and organization in Teams on the web: this helps establish whether the problem is confined to the desktop client or also affects access through the service. Ask your administrator to check service health and open a support case with the client version, reproduction steps and collected logs. Share those logs privately, not in this public thread. Use the web client temporarily if it displays your chats correctly.