Mock LocationI stopped spoofing, but the coordinates stayed the same
This is how apps that cached the last known point behave. Open Mock Location — it will restore the correct state — and fully restart the other app.
A separate situation arises when the firmware killed the app's process in the middle of a session: the test providers stay in the system with the last written value, and no new coordinates arrive. The sign of exactly this case is that the notification disappeared from the shade by itself, although you did not stop spoofing.
Opening the app fixes it: on launch it checks for a mismatch between the saved and actual state, picks up the orphaned providers and either returns spoofing to a working state or removes it correctly.
To keep it from happening again, turn on autostart and remove battery restrictions — more in the question about Xiaomi.