Large playlist switches to playlist radio with no discernible pattern

[mickeyglitter]

Plan

Premium

Country

 USA

Device

iPhone 6

Operating System

11.3.1

My Question or Issue

I have a large playlist (1000+ songs) and have noticed that after a certain number of songs are played, it defaults to playlist radio, sometimes a couple of times a day. I can't figure out how it determines how many songs it will take before the playlist radio takes over. There's no way all the songs on the playlist are being played on a regular basis for the app to shift me over to playlist radio (which BTW I dislike quite a bit) so often. Will turning off playlist radio fix this or is there something in the app that allows only X number of songs to be played?