bummer to hear man! it sounds to me like you’ve had at least a bit of ‘overreaching’ - a failure to elevate HR at intervals and very low mood are excellent indicators of that. it’s a broader picture and you could take other factors into account, but it’s good to evaluate that.
when I read your story, I wonder whether you had more outside / Z2 TSS and that gets you thinking now that you actually do less work. trainer / TR TSS are representing a lot more work than outside TSS. you may actually not have done as bad during training as you think? and when you thought your TSS was relatively lower than before, maybe you felt like you should’ve done more but were actually already against a limit?
for the VO2max workouts, we’ve had some discussions about this. it’s ok to lower the intensity for them as not for all it is 120%, particularly if you fail them consistently. see also here Time at VO2max discussion
it’s great to learn from this though! if you feel like a change, why don’t you mix it up next year and do something else/consider shorter distances, may potentially even help to find another gear. why don’t you even try out a lower volume as well and see how that feels?