This. I’m not usually a fan of scrum, but this is one of the problems it can help solve. You can decide to zig or zag every couple weeks at the end of a sprint,

This. I’m not usually a fan of scrum, but this is one of the problems it can help solve. You can decide to zig or zag every couple weeks at the end of a sprint, but for those couple weeks you’ll hold steady in one direction so that you can make reliable progress (and force the people making changes to sleep on them and bundle them up.) Frankly, though, your PM sounds ineffective - especially in a kanban system. Part of their job is making sure there’s a shippable MVP SOON that you can THEN iterate on IF improving it at that point will have more business impact than building the next feature will. And they’re clearly undermining that effort.