4.5.0
https://codesandbox.io/s/wizardly-pascal-jcom3
see link
I can only reproduce it with UK timezone set
A contiguous calendar.
Days jumbled all over.

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Added images since the bug seem to depend on what timezone you are in which may not be obvious.
Reproduced with UK timezone.
Any updates on this?
@macthestack Sorry. Let me put it to a higher priority.
Thank you.
The situation gets wrong result because of DST.
Fixed in #12172