Storage deals stuck in StorageDealSealing

[vyzo]

Describe the bug
While stress testing storage and retrieval deals with 300 concurrent deals per client, we always end up with the clients stuck in StorageDealSealing without making any progress

To Reproduce
filecoin-project/oni#81

Expected behavior
Storage deals should make progress!

Version (run lotus --version):
lotus master as of this morning: lotus v0.4.2-0.20200703005127-9d56dabb316f

Additional context
Investigating the goroutine dumps from one of the miners, there is an inordinate number of goroutines stuck in github.com/filecoin-project/go-statemachine.(*StateMachine).run, stuck in github.com/filecoin-project/[email protected]/machine.go:53.
There is also a number of goroutines stuck in github.com/filecoin-project/sector-storage.(*scheduler).Schedule, line github.com/filecoin-project/[email protected] 0318-4c1968f62a8f/sched.go:108

Will attach full goroutine dump

[vyzo]

goroutine.dump.zip