Something similar has happened to me in the private lessons I import. (I focus mainly on private content, so no LingQs to share with the support team).
Check your timestamps for each sentence and make sure the timestamps progress chronologically as each sentence of you text is reviewed by you (in edit sentence mode or edit lesson mode.
This is an example of what happens when your timestamping is not consecutive — all the way:
Note: The title “sentence” here had a time stamp of 0:00 - 01:50, so it would highlight the title line with the correct text lines, but not scroll properly as a result.
And make sure no timestamps overlap because the LingQ reader can’t handle sentences that are spoken at the same time, but separated as separate sentences in the audio.