It happened to me twice now. Today for the second time, the last time was a couple (2-3?) weeks ago.
I start a workout, after the warmup, the workout drops to Zone 1 (everything fine so far) and a big zone 4-5 effort would come.
I start ramping up my cadence and the erg mode won’t shift to the new Watt number. No matter what I do, (pause the workout and unpause it, push high watts, push low watts etc.) erg mode stays the same (the old zone1 number). If I stop pedaling completely, the game (or the hub) finally registers that it should switch to the new number and switches.
It worked just fine after that very first big shift from zone1 to zone 4/5 (although there were quite a few more).
Both times this happened it was my first ride of that day, and the first zone1-zone4/5 change of that day. Only on zone1 to zone4/5, and when I have a very high cadence 120+. I think if I keep a lower cadence it works just fine.