panic: ptrace status unexpected: got 31, wanted stopped

goroutine 4605691 [running]:
gvisor.googlesource.com/gvisor/pkg/sentry/platform/ptrace.(*thread).wait(0xc000c365a0, 0x0, 0xd1c3)
	pkg/sentry/platform/ptrace/subprocess.go:323 +0x4b9
gvisor.googlesource.com/gvisor/pkg/sentry/platform/ptrace.(*thread).syscall(0xc000c365a0, 0xc00166ac78, 0xc00166ae20, 0x2, 0x2)
	pkg/sentry/platform/ptrace/subprocess.go:390 +0x10f
DIAGNOSIS:
I0409 04:59:07.035637   36874 x:0] ***************************
I0409 04:59:07.035829   36874 x:0] Args: [/syzkaller/managers/ptrace-proxy-sandbox-race/current/image -root /syzkaller/managers/ptrace-proxy-sandbox-race/workdir/gvisor_root -watchdog-action=panic -network=none -debug -platform=ptrace -file-access=shared -network=sandbox debug -stacks ci-gvisor-ptrace-proxy-sandbox-race-0]
I0409 04:59:07.035913   36874 x:0] Version release-20190304.1-94-gfbe7ba466193
I0409 04:59:07.035970   36874 x:0] PID: 36874
I0409 04:59:07.035994   36874 x:0] UID: 0, GID: 0
I0409 04:59:07.036015   36874 x:0] Configuration:
I0409 04:59:07.036058   36874 x:0] 		RootDir: /syzkaller/managers/ptrace-proxy-sandbox-race/workdir/gvisor_root
I0409 04:59:07.036095   36874 x:0] 		Platform: ptrace
I0409 04:59:07.036132   36874 x:0] 		FileAccess: shared, overlay: false
I0409 04:59:07.036185   36874 x:0] 		Network: sandbox, logging: false
I0409 04:59:07.036241   36874 x:0] 		Strace: false, max size: 1024, syscalls: []
I0409 04:59:07.036270   36874 x:0] ***************************
D0409 04:59:07.036331   36874 x:0] Load container "/syzkaller/managers/ptrace-proxy-sandbox-race/workdir/gvisor_root" "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0409 04:59:07.047370   36874 x:0] Signal container "ci-gvisor-ptrace-proxy-sandbox-race-0": signal 0
D0409 04:59:07.047456   36874 x:0] Signal sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0409 04:59:07.047565   36874 x:0] Connecting to sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0409 04:59:07.050682   36874 x:0] urpc: successfully marshalled 117 bytes.
I0409 04:59:07.495879   36874 x:0] Found sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0", PID: 46332
I0409 04:59:07.495953   36874 x:0] Retrieving sandbox stacks
D0409 04:59:07.495986   36874 x:0] Stacks sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0409 04:59:07.496041   36874 x:0] Connecting to sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0409 04:59:07.496174   36874 x:0] urpc: successfully marshalled 36 bytes.
W0409 04:59:07.539379   36874 x:0] FATAL ERROR: retrieving stacks: getting sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0" stacks: urpc method "debug.Stacks" failed: connection reset by peer
retrieving stacks: getting sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0" stacks: urpc method "debug.Stacks" failed: connection reset by peer