Recently I have been looking for a sale to buy the battle chasers game that came out not too long ago, and this morning I got an email that had battle chasers and then said it was 75% off. Excited, I clicked on the link and it was full price. Is there maybe a delay on some of their sales or something else?

It's just a mistake in the email. The game is new so no chance having a 75% off this soon.

If it is the case, then GOG's email management is really really bad.
Alought GOG's email management was always quite bad already.

At first I thought this was about an "An item on your wishlist is on sale" email, but turns out it was the default newsletter.
It reads "Unmissable premieres: new Grim Dawn expansion, Battle Chasers, and more • save up to 75% on classics in the Weekly Sale" where they put together what happened during the week and list ongoing sales.
According to this, see attached pictures, Battle Chasers and Grim Dawn - Ashes of Malmouth both are on sale 75% off. Seems to me like they changed things around in the layout and forgot to remove the discount panels.
Since it's likely to be a human error, I don't expect this to happen more frequently, though I agree that it shouldn't have happened and I understand your frustration thomas663.

Have to say I noticed that too, though assumed it was an error even before clicking it as it's been a reasonably hyped game release and it would have to have been an absolute flop to be selling at that discount already.