Growing subtitle drift can result from a different edit, frame-rate interpretation or timing conversion. A fixed delay only moves every cue by the same amount, so it cannot reliably repair a changing offset. Compare early and late dialogue before deciding what kind of correction is needed.
Map the change
Note whether the mismatch grows steadily or jumps suddenly at a particular scene. A steady change suggests a timing-rate issue, while a jump can follow an added recap, advert or cut. These are useful clues, but they do not prove a cause without comparing the actual video and text versions.
Avoid repeated manual chasing
Moving the subtitle delay every few minutes can make the programme watchable temporarily but hides the overall pattern. Keep a record of one early and one late example. If an alternative supplied track exists, compare it without changing the audio or picture timing, which may already be correct.
Request a matching track
Provide the title, episode, selected language and approximate times where the offset differs. Do not assume a subtitle file for another release is interchangeable merely because the name matches. A properly matched track is preferable to a series of local adjustments, particularly for a shared device where the next viewer may inherit the altered delay.