We have had 3 very mild winters so far in Berlin, it has rarely been below freezing for more than a couple days and in 2017 year we had a rose bloom in the garden in December.
I have a white Japanese import Ume which always seems to flower early and the first bud broke last year in December. the photo here is from the January 11th 2020 and it has again started on Jan 1st.
Oddly enough I have another one which I am field growing since 2013 and it held its leaves until December 30th.
all the rest of mine are pink flowers (about 6 trees) loose leaves in November with flower bud break at end January beginning February. These 6 were either field grown by me from Chinese cuttings or Japanese imports.
wondered when yours open where you are?
I assume the flower bud break in Dec/January of the one Ume is due to global warming (we have that here unlike the US because Merkel belives in it where as Trump does not )