My server has some player stats, but it is not including all of them. How does this get fixed?

There are no known issues with the recording of player statistics.

Players will only be recorded if they have a score.
No score = nothing to record.

AI bots are never knowingly recorded.

A player must play long enough to have been scanned at lease 2-3 times (with a score) within the game. This may require the player is in the game for between 8 and 20 minutes before being recorded in statistics.

Thank you for the information.

Here is the situation: I was in the server for over an hour yesterday afternoon was listed in the online player section, however it didn't record my score (and I had a score as I completed a round of checkpoint in Insurgency Sandstorm).

Then my husband and I (we own the server) were in it again for another hour last night. It showed us in the online player section, he had a score of 310 and I had 0. When we were done, we thought it would update and we'd show up in the Top Players section, however we did not and still have not.

This is my Server: https://www.gametracker.com/server_info/108.61.100.220:27025/

As you can see now, the scanners did register your appearance over 2 days.
The Top 10 Players can take a while to update. Admittedly, 1 - 2 hours is more normal.

As I said above, the system works by scanning your server occasionally.
Most games have a report API (application programming interface) that allows an external server to query the game server.
Gametracker scanners are only able to report what is returned to them by the game server.
Owing to network traffic and server loads, at either end, the scanning system is less than perfect.

It does though appear to be working more or less within expected tolerances.

Yes, thank you so much! It does appear to be working now. =) It was just weird to see other players registering and we weren't.