In https://drafts.csswg.org/css-grid/#auto-tracks

If multiple track sizes are given, the pattern is repeated as necessary to find the size of the implicit tracks. The first implicit grid track before the explicit grid receives the first specified size, and so on forwards; and the last implicit grid track before the explicit grid receives the last specified size, and so on backwards.

Note the usage of before. I think the first one is intended to read “after”, right? That would make sense and that’s also what Chrome has implemented (Firefox doesn’t seem to support multiple track sizes in these properties). Test case attached.