BUG: v4.7.1221 takes 4 times as long to process heavy threaded tests than v4.6.519

[ghost]

Hi, we have some tests that tests that usually takes around 5 minutes to run in total, but when using opencover 4.7.1221 it takes 20 minutes.
Downgrading to v4.6.519 makes the tests pass in about ~5 minutes - but then no coverage is returned (that's an issue for another time).

We've just started to use OpenCover and the results we've got are from a previous solution where we run our tests through another tool. It seems that the more the tests rely on multithreaded workloads the more the test time for a test is hit, in other words high workload = high delay of test time using opencover.

We are using .net framework 4.7.2 for the projects