Laggy replays could be caused by various factors. Here are the reasons most likely causing this:
1. Your device is not up-to-date with its system software. (MOST COMMON)
2. Your internet connection is not stable.
3. Your phone is low on storage/ram.
I recently have had extremely laggy replays on iPhone however a quick update to the latest software (iOS 18.1.1) solved this instantly.