Uncap the server's framerate to something like 1000fps via limitFPS and you can see diag_frameNo returns the same number for multiple EachFrame executions.
This might also only show up while the server has been running for multiple hours before becoming inaccurate.
Execute the following on the server after running it for a few hours and observe diag_frameNo returns the same value over multiple executions
[] spawn {
private _id = addMissionEventHandler ["EachFrame", {diag_log format["fn(%1) date(%2)",(diag_frameno toFixed 0), systemTime]}];
sleep 1;
removeMissionEventHandler ["EachFrame", _id];
};Nvm, I am dumb and I realize the mistakes in trying to represent the large value misled me