Sudden sharp form drop off!?

Why has my form suddenly dropped off in the last few weeks?

Summer/Autumn: I had a decent training plan up until 31 October when I had a couple of bone fractures, putting me off the bike for pretty much all of November. Until that point I was around 350-355W for an hour (4.6wkg).

November: Off the bike apart from gentle turbo sessions

December/early Jan: Solely indoor rides since then, including mainly 15mn fullgas sessions and 45mn fullgas sessions. Plus some Z2. Initial post-recovery signs were great and by start of January I was back up around 355W for an hour again and 375W for 25mns, feeling fresh.

Since around mid-Jan I have noticed a significant drop in power, with even holding 360W for 20mns being relatively tough. I have taken a lot of rest days in Jan to try to recover but have not come back particularly strong.

My conclusion is that in Dec/early Jan I was reaping the rewards off a strong summer/autumn training plan plus a decent break in November, but that my combined volume/training load in December was not sufficient to continue the gains and I did not follow a structured plan in that time either. Which makes sense but I did not expect such a sudden/sharp drop off as a result of that and I was experiencing steady improvement till then. Any thoughts?

I have added my training zone profile as an attachment.