We sometimes see failures with an empty fail report, as in:

Isolate (/b/s/w/itTbo578/dart_fuzzYMJHUK) FP : JIT-O3-ReleaseIA32 - JIT-noVFP-ReleaseSIMARM: !DIVERGENCE! 1.15:2617449246 (ResultCode.error vs ResultCode.success)

fail1:

Most of the time these don't reproduce locally. We should find out what those are, probably with some more elaborate logging.