In a theme league, my team settings are to rest the starters with a lead of 6 or more runs after the 7th....
I usually don't check box scores or read the play-by-play but in a recent game, sparky put in 2 bench players to 'rest the starters' with a 1 run lead in the 8th. Why would it does this?

I would like to keep the player rest settings as they are bc of the certain requirements in this particular theme that won't get into, but I don't want bench players coming in during a 1 run game in the 8th again.

Could you post a link to the box score to take a look at?
or
say which team and game?

What is your defensive replacement setting? The game text will say "rest the starters" whether it is invoking the "rest with a big lead" rule or the "replace my crappy fielders when the game is close" rule.
Were the original players in your lineup pinch-hit or pinch-run for? If the players were pinch-hit or pinch-run for, the game text will often say "rest the starters" even though all it's doing is finding somebody to play the required position.

If you're referring to the 11/23 AM game of your Charleigh and the Whipadors team, that's exactly what happened. Raines and Reyes were pinch hit for and had to be replaced.

Your "rest players when leading" setting does not take precedence over your PH/PR settings. If you don't want this situation to happen you have to either (a) reduce the PH frequency in your manager settings and/or (b) uncheck the PH box in advanced settings for players you don't want to be taken out of the game.

General rule for SLB: your settings are never randomly disregarded by the algorithm. Whenever something happens it is for a reason.

I guess that didn't register with me at 2am.... I'm not sure what I was thinking