If I sort my transaction list by date (descending) and scroll down to a couple years ago there is a point where it switches from grouping by month to grouping by year. However, I noticed that some transactions that should be in the last month grouping appear in the first year grouping.
Here's what I see. There are several October, 2023 transactions that appear in the 2023 group despite there being an "October 2023" group above it.
Maybe it's just a coincidence but it looks like up to today's calendar date (October 5) is put into the 2023 group and the following transactions are put into the month group.
Anyways, I'd expect all transactions for October, 2023 to appear in the group "October 2023" and those from September 30 back to January 1 to be in the "2023" group.