I have just spent 2 hours trying to figure out why since last night I have had exactly the same thing
Although the "lock screen" had no 3 dots at all couldn't get rid of it and it was driving me mad read all the above answers and for me it was a third party keyboard called kika..had no trouble with it before but it updated last night
I guess the moral of the story is beware of heavy advertised "free" apps. Yes of course the Devs need revenue but they should at least warn you or give you the option to donate!