Similar style as me. What I have noticed though is even if the workout asks for x cadence (say 110) even if I can't spin that high as legs are fatigued so long as maintain the target power the workout is happy and I still get the star.
After reading other's replies I think I have also spotted why I don't have the spiral of death any more, and I think it's that I've learned how to avoid it .... whatever you do, don't stop pedaling; as soon as you do the ERG resistance rockets and you're in the spiral. I take drinks in the rest periods only so I don't lose focus in hard sections. I never let the cadence drop below 50. if I'm struggling I'll drop the session down from 100% (or if feeling good, push it up above 100%). If I know there is a very hard section coming up and I really can't make it as not had enough rest I'll pause the workout, spin my legs out for a minute, get the cadence back up, then continue the session; I rarely do this, but when needed it's the difference between failing a session and being able to finish a session.
Final thing I've learnt is the FTP that Zwift gives me from racing is a little too high for the workouts. Zwift has me at 257 FTP, but there is no way I could finish the workouts at this FTP. I've therefore set the workouts at 240 watts and I can always go up from there 10% in session. I do this on some of the easier sessions, but on hard sessions like Yellow Unicorn I had to come down to 95% for the last 10 minutes - had I been at 257 FTP I'd have failed that session!
These are my top tips anyway .... peeps are free to ignore or use as they see fit