[Bug-Candidate]: Inconsistent "thread blocked indefinitely in an mvar operation"

[0xicingdeath]

Describe the issue:

An inconsistent Echidna failure on Curvance identified the following "thread blocked indefinitely in an mvar operation" that we got intermittently throughout the engagement. This would occasionally result in jobs failing on the cloud. I don't have a whole lot more information on what cause(d) this specific error.

Code example to reproduce the issue:

Occasional runs on Curvance resulted in this error.

Version:

Error was last seen on Echidna 2.2.3 once, and one of the branches containing fixes for Echidna.

Relevant log output:

No response

[zaqk]

I'm also seeing this error frequently on an M1 Macbook

[samalws-tob]

Anyone who's getting MVar errors: please run the catchMVarErrors branch on your codebase and tell me whether any "[MVar]: Error at ..." message appears before the normal "thread blocked indefinitely in an MVar operation" error message. This should help to pinpoint the cause of these problems