@Charlatan @octavious230 If you really want to lock in a particular batting order, or just lock a player to a particular spot in the order, you can do it. More on this in a sec. But first:
I assume you clicked “submit team” after making your changes? If you make changes and the game runs a sim before you “submit,” the game forgets your changes. But you probably know that.
If you’re sure you did click “submit team,” then check your depth chart. Have you assigned backup players to each position, and told the game how often to play the backup? If any starter is tired, there’s a chance he’ll be subbed out. Even one substitution can lead the AI to change your lineup; e.g., if a high-contact hitter is replaced with a power hitter, or a speedster replaced with a slowpoke, the AI will likely change the lineup order.
Personally, I generally like the lineup changes the AI makes for me when a starter subs out. E.g., recently Gedman sat for a day, and my lousy substitute catcher was swapped in – and the AI had him bat 8th, not in Gedman’s #5 position. Pretty good.
If nonetheless you want more granular control over where every player bats, then there are a couple options. One you probably know about already: 7-day lineups. You can tell the game exactly who you want to start in what position (including pitcher) for the next 7 days. Not the next 7 games – just the next 7 days. If you leave “clear 7 day lineups” unchecked, then the game will keep your 7-day schedule intact in perpetuity, which might work okay, if your 7 day lineup rotates starters in and out for fatigue. Personally, I don’t use 7 day lineups in PT, because I check the game only once or twice a real-life day. (Yes, PT needs a 30-day lineup feature.)
But OOTP 20’s PT features a new way to lock in a player – or all players – to lineup spots. If you go to a player’s screen and set his Game Strategy, you’ll see you can lock him to a spot in the order. So if you want so-and-so always to lead off, you set his order spot to “1,” and he’ll always lead off. Supposedly. I haven’t tried it because I generally like the way the AI handles my subs. (In the name of science, I’ve just tried it; will report back.) Also, you can force a player to play a position, using the same screen.
Hope this helps.