Regression introduced here:
xunit/assert.xunit@bb5d19d#diff-5ddb02071f63a19de4084075b7e4e26c92234035da84fc639d197f2b2ce1dd4cR65

It looks to me like this should return rather than fall through to calling compare.Equals again. It might even be further simplified as this: ericstj/assert.xunit@c195a15

Here's a repro for the failure
xunitEnum.zip