According to Raul Arabaolaza there are possible problems running the PCT with a version of maven prior to 3.5.4. The current jenkins/pct image is built on 3.5.2.
Basically, plugins using incrementals. They need 3.5.4 with lower versions the PCT is not going to be able to compìle them and as no tests are run is difficult to realize unless you look at the HTML report
Fixed with https://github.com/jenkinsci/plugin-compat-tester/pull/81