Users sometimes want to copy and paste in external text into the transcript editor.
We recommend not to do this in the transcript editor.
You can do this in the visual subtitle editor.
the text you are copying in, say from Word, has no timecode attached to it; it is simply plain text. While the words in a SS transcript has timecode attached to it. When you overwrite that, you overwrite the timecode.
The visual subtitle editor is focused on the start and end times per subtitle card; the timings per word matter less. So you can copy and paste text in here and you will still get a well-time subtitle file.
If you made a mistake and you copied text into the transcript editor and have lost the timing per word:
Use the version history feature to revert back to the original transcript. Then export to the visual subtitle editor and paste text in there.