Client stops working with `Observer job lock acquiring timed out.`

Hi,

Client (1492) stops working after some time with "Observer job lock acquiring timed out"

Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:   File "/var/lib/satnogs/lib/python3.7/site-packages/satnogsclient/waterfall.py", line 108, in plot
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:     tmin = np.min(self.data['data']['tabs'] / 1000000.0)
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:   File "/usr/lib/python3/dist-packages/numpy/core/fromnumeric.py", line 2618, in amin
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:     initial=initial)
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:   File "/usr/lib/python3/dist-packages/numpy/core/fromnumeric.py", line 86, in _wrapreduction
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]:     return ufunc.reduce(obj, axis, dtype, out, **passkwargs)
Dec 06 13:12:56 satnogs-receiver satnogs-client[351]: ValueError: zero-size array to reduction operation minimum which has no identity
Dec 06 13:17:39 satnogs-receiver satnogs-client[351]: satnogsclient.scheduler.tasks - ERROR - Observer job lock acquiring timed out.

{
    "versions": {
        "satnogs-client": "1.4",
        "satnogs-client-ansible": "202010161917",
        "satnogs-flowgraphs": "1.2.2-1",
        "gr-satnogs": "2.1.2.1-1",
        "gr-soapy": "2.1.3-1",
        "gnuradio": "3.8.2.0-2",
        "satnogs-config": "0.11"
    },
    "state": {
        "is-applied": true,
        "pending-tags": null
    },
    "system": {
        "date": "2020-12-07T12:23:09.326980+00:00",
        "distribution": {
            "DESCRIPTION": "Raspbian GNU/Linux 10 (buster)",
            "RELEASE": "10",
            "CODENAME": "buster",
            "ID": "Raspbian"
        },
        "pending-updates": true,
        "platform": {
            "system": "Linux",
            "node": "satnogs-receiver",
            "release": "5.4.72-v7+",
            "version": "#1356 SMP Thu Oct 22 13:56:54 BST 2020",
            "machine": "armv7l",
            "processor": ""
        },
        "memory": {
            "total": 1021706240,
            "available": 398069760,
            "percent": 61.0,
            "used": 560455680,
            "free": 193245184,
            "active": 571830272,
            "inactive": 205594624,
            "buffers": 16748544,
            "cached": 251256832,
            "shared": 10629120,
            "slab": 29605888
        },
        "disk": {
            "total": 7594229760,
            "used": 4167872512,
            "free": 3070353408,
            "percent": 57.6
        }
    },
    "configuration": {
        "satnogs_antenna": "RX",
        "satnogs_api_token": "[redacted]",
        "satnogs_gain_mode": "Settings Field",
        "satnogs_other_settings": "IFGR=20,RFGR=1",
        "satnogs_rx_bandwidth": "600000",
        "satnogs_rx_samp_rate": "2000000",
        "satnogs_soapy_rx_device": "driver=sdrplay",
        "satnogs_station_elev": "23",
        "satnogs_station_id": "1492",
        "satnogs_station_lat": "52.4937782",
        "satnogs_station_lon": "13.4483546"
    }
}