What was unusual about the grievers in Ch.44? Why do you think the Maze was no longer changing each day?

The griever's activity was unusual because they no longer paid attention to the runners. They simply ran past them and disappeared. We can infer from the text that the game was changing.

"Minho spotted a Griever disappearing around a corner ahead of them; and it didn't come back. Thirty minutes later, Thomas saw one do the exact same thing. An hour after that, a Griever came charging through the Maze right past them, not even pausing. Thomas almost collapsed from the sudden rush of terror."

The Keeper sighed. "I think the Creators want us to know there's no way out. The walls aren't even moving anymore — it's like this has all just been some stupid game and it's time to end. And they want us to go back and tell the other Gladers. How much you wanna bet when we get back we find out a Griever took one of them just like last night? I think Gaily was right — they're gonna just keep killing us."

Thomas didn't respond — felt the truth of what Minho said. Any hope he'd felt earlier when they'd set out had crashed a long time ago."