Describe the repeat boundaries
Note the timestamp where playback jumps back and the timestamp it returns to. A repeat between stable points is a different observation from a whole file restarting or a playlist beginning again. Keep those boundaries with the file and installed mpv version.
The stable manual distinguishes A–B looping, single-file looping and playlist looping. It also warns that user input configuration and scripts can change keyboard bindings. A remembered shortcut from another player front end is therefore not proof of the command currently assigned to that key.
Check the active command and points
In mpv’s documented defaults, lowercase l cycles the A–B command: first it sets A, next B, then clears both. Uppercase L has a separate infinite-loop function. Inspect the on-screen state and actual binding before pressing repeatedly, because an extra command can create a new point after the old pair is cleared.
If a deliberately configured A–B loop will not start, check that both points are set and that ab-loop-count is not zero. The manual explicitly says zero disables the loop even when both timestamps are present. Record those values rather than interpreting the same controls as a connectivity test.
Verify normal progress after clearing
After clearing an unintended pair, let playback cross the previous B point without manually seeking past it. The manual says a manual seek beyond B does not trigger the loop, so that action alone is an incomplete comparison. Observe whether normal forward progress continues.
For help, provide the two timestamps, active bindings or relevant configuration and whether the file, whole playlist or only the marked segment repeats. Keep private media locations out of public notes. This preserves the difference between a player’s deliberate repeat state and a programme source that actually stops advancing. It also prevents repeated network changes from obscuring an input action that already explains the repeat.