I had an issue reported by the remote friends/family where emby direct play media would be delayed about 50 seconds before it starts. Transcoded media was all fine. This only affected Emby. I installed and configured a new emby server and had exactly the same thing. After a week of checking everything, and posts to the emby forums, it seems that there are a few others with the same issue at the same time of end Aug (Maybe around 25th). The issue is fixed by turning on development mode. Everything has been stable for years and nothing changed by me on my system, I was even not home when this happened. Two users in Australia and one in Canada, however I will post on the emby forums to see if anyone else has reported.
Further review and analysis from other cloudflare technical people suggest something changed at Cloudflare that affects the way caching works that causes this issue in emby. They will raise a support ticked for the exact detailed issue. In summary, if caching is active, cloudflare is some how stripping the range header from mkv’s. To resolve, I have have turned caching back to standard, and then have added a page rule line that bypasses the incorrectly cached objects