Great points and thanks for having such a detailed look.
Initially, the ramp test was planned on tuesday after a day of rest. The sunday before a 2 hour endurance ride was planned. However, the weather was nice and I joined a club, so I joined them on a ride instead, which was indeed much more intense and longer as initially scheduled. For that reason I put the Ramp test to wednesday instead and did an easy ride on Tuesday (not a race 
average HR of 132, I was just talking and reading some stuff on my mobile phone). I took that as a sign I was recovered.
Some fatigue is however a definitive possibillity that can’t be excluded. But would that lead to such drastic reductions in Ramp test performance?
Thanks a lot for the suggestions on the training plan!
I am a bit afraid of pushing planned training out of the way for the sake of testing. In the end we use the numbers only to get the training right. I am not sure about skipping workouts just to perform well in a test to be honest. Is that really worth it? I was planning on redoing the ramp indeed, but without powermatch this time, and record the Quarq data seperately.
I still wanted to do the London stage of the Tour de Zwift (last month of membership). What if I just do that one instead of Palisade and keep my power around 200 for the duration instead of pettit? Then have a rest tomorrow, and do the ramp on saturday, and if that goes well, ride for 15 minutes at recovery and add a shortened palisade after to keep a bit in line with the structure of the plan?