"IRIS can not become quiescent" error

Did anyone run into this error when stopping a Production from Ens.Director?

Ens.Director::StopProduction => ERROR <Ens>ErrProductionNotQuiescent: IRIS can not become quiescent

It happens sporadically when an automated unit test from a class that extends %UnitTest.TestProduction runs a test on a Business Process. I already increased the parameter MAXWAIT to 30 seconds, but the error still happens.