Text threads suddenly creating new and separate thread

I recently updated my iPad Pro to software version 17.6.1. Now text conversations that have been going on for years are suddenly in a new thread with my name at the top. I have deleted those new threads and asked for a response in the old thread - and a new thread appears. Happened in one conversation last night. Suddenly a new thread from the same person - again with my name on the top. My iPhone works fine - it’s just the iPad which I have been using for years. Brand new issue. I have restarted iPad several times.