Yeah there's a clear issue even without auto repeat.
Just a simple grid with 1 column like:
  grid-template-columns: [a] 100px [b];
If you add an implicit column before it that ends up being 50px width for example,
the computed style of grid-template-columns would be:
  [a] 50px [b] 100px

But the elements placed using "a" or "b" are correctly positioned.
So the problem seems to be only on CSSOM.

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