Hi @SLR2009, we had a mild winter here also and very wet. Tbh I think you have already hit the nail on the head so to speak. The trees need a cold winter to go to sleep properly. I have seen a lot of maples this Spring that are similar to your photo. You may get a second flush if the branch is alive and showing green underneath the bark, ie fingernail test. Also the very wet Spring has caused 'a lot' of problems with our small maples , whereby the roots have been sitting in water for a long period. Something they DO NOT like. Oxygen starvation and root rot then occurs which shows up above in dead branches or troublesome to slow leafing out. Anyway give it a few weeks to at least the middle of June and give the soil around its base a light pricking to relieve soil compaction 'now'. Hope that's of some help.
