When you click to SHUFFLE tracks, there are 3 options. Shuffle is ticked obviously, but what exactly does separate artists do. Also when and why would you use clear played flags?

Usually you want to do all three.  sometimes you'll notice my saying "50 passes, artists not fully separated".  that means it can't do a good full spread of some artists in that category.  so shuffle a few more times. you'll get the message each time.  then scroll up and down the list and if you see some songs  by same artist close together, you can manually move them/spread them apart. ........Clearing Flags:  each time a song is scheduled, M1 marks it as played in the then 'current' pass thru the list.  when every song has been scheduled, m1 goes to the top of the stack again and begins working down the category again.  it will not repeat/schedule any song until every song has been scheduled.    now, lets say you have 50 songs in a category and when you finished  scheduling the Friday list the last song scheduled from the category  at 11:45pm was the song that was in rank position #48.   You shuffle and  don't clear the flags. the song that was in position #49 before, now after the shuffle moves to rank position #3.  You start to schedule Saturday. the only two songs without "played flags" are songs that were (formerly) in positions #49 and #50.  So they both get scheduled right away....but then, after those to are scheduled, then M1 internally clears the flags and begins at the top of the stack again...thus the song that WAS as #49 before the shuffle, is NOW at #3 and as M1 starts at the top of the stack again, it will quickly be eligible for another schedule and it is much, much sooner than it would normally come up in rotation.    On the other hand, say you shuffle and you DO clear the flags. the song that was at position #48 had just gotten scheduled at 11:45pm Friday.  After the shuffle it moved to position #2.  The  flags were 'cleared', so M1 starts scheduling Saturday at the top of the list in the new card-stack order.  The song now at position #2 gets scheduled again right away.

The bottom line on this is the next 'pass' thru a category after a shuffle is always going to have some weirdness to it.  If the category normally has a 3 day turnover, some of the songs in the category are going to be scheduled much sooner from their last play, some are going to be scheduled much later than they'd  have come up normally had you not shuffled.    This will happen whether or not you clear the flags because the card stack/rank order changes.  So, I recommend shuffling only on weekends, because weekend listening patterns are so very different from weekday patterns.  Listeners are less likely to notice a 'quick repeat' of some songs when it happens on weekends because the Weekday Listeners are mostly not there.  And I always clear the played flags when I shuffle.