Invalid WebVTT files
If you ingest an invalid WebVTT file using the Dynamic Ingest API, the operation will succeed and the file will be added as an asset to the video. However, the captions or chapters will not work in the Brightcove Player and will prevent other valid WebVTT files associated with the video from working as well.
Workaround
You can validate your WebVTT files using this online validator.