The problem is that iOS doesn't differentiate between a call that merely checks for the presence of a clipboard entry (e.g. so you can enable "Paste" in a menu/submenu) and actually copying the contents of the clipboard.

The workaround (for legitimate apps) is to simply always keep that "Paste" option enabled--even if the clipboard is empty. That way you won't freak out your users and only suffer the most minor of usability consequences.

Having said that I don't think TikTok has any relevant functionality such as enabling a "Paste" option so... Most likely nefarious!