I already uninstalled the plugin, and found the solution with snippet but I can briefly comment, that when the code of your plugin was implemented, somehow part of the text is visible and only part of it hides and the arrow is in the bottom of the text not at the top as it should be when the text is collapsed, something like that:
text text text text text text text text text text
text text text text text text text text text text
(only part of the rest text collapsed)
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I hope this helps.
Because here it looks like working perfect: https://www.youtube.com/watch?v=4n2vPjulBZU
But my experience was as described.