Since some undefined point of time in the past (5 years ago? since dawn of time?), Windows buildbot had only ran a fraction of default tests (i.e mysql-test-run.pl --suite=main,innodb,plugins).
In the meantime, one can assume other suites got broken, since they were not tested. In addition, more default tests suites were added to mtr, and none of them were tested (buildbot continued to run main,innodb,plugins)
A change in buildbot configuration was made to run tests per repo ( if mysql-test\collections\buildbot_suites.bat exist, it will be used to run the tests). We can use it to add more suites, once fixed. The goal should be to fix suites such that default suites would run without errors.