panic: ptrace status unexpected: got 31, wanted stopped

DIAGNOSIS:
I0425 04:29:12.477277    7296 x:0] ***************************
I0425 04:29:12.477450    7296 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]
I0425 04:29:12.477516    7296 x:0] Version release-20190304.1-140-g99b877fa1d6f
I0425 04:29:12.477547    7296 x:0] PID: 7296
I0425 04:29:12.477575    7296 x:0] UID: 0, GID: 0
I0425 04:29:12.477604    7296 x:0] Configuration:
I0425 04:29:12.477619    7296 x:0] 		RootDir: /syzkaller/managers/ptrace-proxy-sandbox-race/workdir/gvisor_root
I0425 04:29:12.477648    7296 x:0] 		Platform: ptrace
I0425 04:29:12.477704    7296 x:0] 		FileAccess: shared, overlay: false
I0425 04:29:12.477730    7296 x:0] 		Network: sandbox, logging: false
I0425 04:29:12.477759    7296 x:0] 		Strace: false, max size: 1024, syscalls: []
I0425 04:29:12.477812    7296 x:0] ***************************
D0425 04:29:12.478003    7296 x:0] Load container "/syzkaller/managers/ptrace-proxy-sandbox-race/workdir/gvisor_root" "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0425 04:29:12.488164    7296 x:0] Signal container "ci-gvisor-ptrace-proxy-sandbox-race-0": signal 0
D0425 04:29:12.488339    7296 x:0] Signal sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0425 04:29:12.488397    7296 x:0] Connecting to sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0425 04:29:12.489070    7296 x:0] urpc: successfully marshalled 117 bytes.
I0425 04:29:12.763938    7296 x:0] Found sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0", PID: 49299
I0425 04:29:12.763998    7296 x:0] Retrieving sandbox stacks
D0425 04:29:12.764182    7296 x:0] Stacks sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0425 04:29:12.764260    7296 x:0] Connecting to sandbox "ci-gvisor-ptrace-proxy-sandbox-race-0"
D0425 04:29:12.764426    7296 x:0] urpc: successfully marshalled 36 bytes.
W0425 04:29:12.806949    7296 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