Our website has around 260,000 to 300,000 sessions each day. There had 4 days that the historical data is zero but Real-Time works correctly.
Here is a summary of what I know and have checked:
- Real Time reporting is working.
- GA reports no problems with tracking code, neither does tag manager.
- We haven't changed any code and nothing has changed on the server apart from increased resources (CPU and RAM).
- A subdomain on the same server with a different GA account is reporting fine, although this site has only a tiny fraction of the traffic on our main site.
- I am not using a filtered view (and I have checked I am looking at today's date!).