We discovered that content in the RiverLand News Channel was being deleted due to an accidental auto-clean setting. Despite turning it off and monitoring for some days the issue persisted (possibly a Telegram bug).
As a result, we created a new channel on September 12. After a week of monitoring, we found the issue still existed, so we’ve decided to stop using the RiverLand News Channel (its content has been cleared, and the name has changed).