I just feel sure that yuma is scum. I have no extra information. But he is acting scummy. A scum narrative explains his behavior. I also expect scum!Galzria to lurk and replace moreso than I would expect town!Galzria too. Or, more accurately, if Galzria was in a game and he was too busy to play out day 1, and he was town, and he thought he was going to survive on his rep, he might be ok just lurking it, contributing whatever happened to pop into his head, and committing to play harder the next day.
Now what if Galzria is scum and he doesn't have time to play day 1? Galz carefully plans his scum play, I think maybe he decided if he couldn't play scum up to his usual standard he would replace out, especially if his partners were taking heat and he felt like he needed to save them. So he replaces. Yuma suddenly finds himself in a scum team in a terrible position, and not much time left on the clock, so he springs into action with a half-baked plan to save his partners day 1 and to work out day 2 later. It makes sense to me.
And what does he do day 2, when we have a slam-dunk lynch on Walrus based on the only kind of investigative result we have? immediately tries to divert us from it. yuma, why shouldn't we lynch Walrus?
So maybe Walrus got roleblocked and NK'd and Walrus isn't scum. Or maybe scum got roleblocked and Walrus is scum. Or maybe sudgy changed his mind and didn't target Walrus and Walrus did target scum. But Occam's razor to me, especially given Walrus's scummy claim yesterday, is that Walrus is scum.