What are these hidden characters? (ID crashes if I GREP search for them)

Hi

I've pasted some old Indesign CS3 content into my ID 16.4 document, and I see these unfamiliar hidden characters at the beginning of paragraphs, and they're causing some issues with my usual typesetting processes.

They look like uppercase "I" characters, and when I paste them into GREP search, they appear as "~I"

If I search for them using GREP, Indesign crashes.

Is there a way to remove these?

Thanks

Richard