11.1 type confusion?

Hi All.
Im trying to bring rescript-parser to latest and seeing this error:

  This has type: t<('a, 'b) => 'c>
  But this function argument is expecting: t<('a, 'b) => 'c>
  These two variant types have no intersection

uh…?

Any hints?
I had just gotten past one where an Array reduce was refusing to flatten to a single type as well:
(('a, 'b) => 'b, 'a, array<'a>): 'b should trivially become (('a, 'a) => 'a, 'a, array<'a>): 'a but solved this with a new function with explicit type annotation.