backend crash

The backend has crashed:

Aug 29 21:04:37 polyanthum rdsys-backend[64122]: panic: send on closed channel
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: goroutine 708 [running]:
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: gitlab.torproject.org/tpo/anti-censorship/rdsys/pkg/core.(*BackendResources).propagateUpdate(0xc000210058, {0x992da0, 0xc0007bda00}, 0x3)
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/pkg/core/backend_resources.go:130 +0x4b1
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: gitlab.torproject.org/tpo/anti-censorship/rdsys/pkg/core.(*BackendResources).Add(0xc000210058, {0x992da0, 0xc0007bda00})
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/pkg/core/backend_resources.go:76 +0x85
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: gitlab.torproject.org/tpo/anti-censorship/rdsys/internal.reloadBridgeDescriptors(0xc000226008, 0xc000210058, 0xc0001f8c70)
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/internal/kraken.go:274 +0xa77
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: gitlab.torproject.org/tpo/anti-censorship/rdsys/internal.InitKraken(0xc000226008, 0xc00042e420, 0xc000127500, 0xc000210050)
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/internal/kraken.go:61 +0x28c
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: gitlab.torproject.org/tpo/anti-censorship/rdsys/internal.(*BackendContext).InitBackend.func1()
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/internal/backend.go:127 +0x99
Aug 29 21:04:37 polyanthum rdsys-backend[64122]: created by gitlab.torproject.org/tpo/anti-censorship/rdsys/internal.(*BackendContext).InitBackend in goroutine 1
Aug 29 21:04:37 polyanthum rdsys-backend[64122]:         /home/user/dev/rdsys/internal/backend.go:124 +0x56d