Identify the exit action that occurred
Note whether the player was closed through its normal quit key, a window button, the documented watch-later quit action or an abrupt system shutdown. These actions do not all promise the same opportunity to save a position. Keep the exact file and approximate exit timestamp with the observation.
The stable manual gives ordinary lowercase q and uppercase Q different roles. The latter saves a position for later playback where possible. It also warns that custom input bindings and scripts can change the commands behind a key, so check the actual binding in a customised installation.
Inspect automatic-save and resume preferences
mpv’s save-position-on-quit option can save when the player is closed through another normal route, such as a window button. The manual says it is disabled by default and that an abrupt termination can prevent saving. Moving to the next playlist item is also distinct from quitting with a saved position.
Keep restoration separate from writing the record. The resume-playback preference controls using saved information when the file opens again. A complete comparison therefore checks the exit action, whether a record could be saved and whether restoration is enabled, rather than assuming one preference governs all three stages.
Reopen the same permitted sample
Use a seekable authorised file, stop at a recognisable position and quit through the intended supported action. Reopen that same file and observe the result. Avoid changing the source path or replacing the file during the comparison, because that introduces a different identity question.
For help, report mpv version, exit action, relevant save/resume preferences and the before-and-after position. The manual also describes saving some changed track or playback settings alongside position, so note any restored language choice separately. These details distinguish a normal unsaved exit, interrupted shutdown and a saved record that was not restored.