Two copies of Sierra Chart running at once in Sierra Chart

What is causing it

More than one instance of the platform is running against the same data folder, or you are running it in more than one place against a service that permits only one connection.

Why this happens

Chartbooks, settings and downloaded data all live in a data folder. Two instances sharing that folder will both write to it, and whichever saves last wins, which is how carefully arranged chartbooks quietly disappear.

Separately, most data services license a single simultaneous connection per user, so a forgotten session elsewhere can knock out the one you are sitting in front of.

The fix, step by step

1. Check whether a second copy is already running before starting the platform, including one left running on another machine or a remote desktop.
2. Close the extra instance, then reopen the one you intend to use.
3. If you genuinely need more than one instance, set it up properly with a separate installation and data folder rather than launching the same one twice.
4. Check with your data provider whether your subscription permits simultaneous connections, since many allow only one.
5. If chartbooks have been overwritten, restore from your backup rather than trying to repair them.

How to confirm it is fixed

Only one instance is running, chartbook changes persist correctly, and the connection is stable with no unexplained disconnections.

Stopping it happening again

Keep to one instance, close remote sessions properly rather than disconnecting from them, and back up chartbooks.