Maintaining message order in large-scale chat applications is a complex distributed computing problem that becomes more challenging as the number of users, traffic, and backend servers increases. Coordinating multiple chat users, managing retries and timeouts, and synchronizing across devices and users are some of the main issues that arise when scaling chat applications. To address these challenges, developers can use techniques such as unique identifiers and sequencing, buffering, windowing, and watermarking, concurrency and load distribution, handling retries and deduplication, and other architectural considerations. Ultimately, teams must balance the need for control and customization against resource limitations when deciding whether to build chat functionality in-house or use existing platforms and libraries.