Some of my machines cannot be reached as client with crowdrender (..connection failed..). On these machines I see the following error in the console after starting blender.

Read prefs: C:\Users\andre\AppData\Roaming\Blender Foundation\Blender\2.82\config\userpref.blend

found bundled python: C:\Program Files\Blender Foundation\Blender 2.82\2.82\python

register_class(...):

Warning: 'CloudIssuesList' doesn't contain '_UL_' with prefix & suffix

register_class(...):

Warning: 'NodeReportList' doesn't contain '_UL_' with prefix & suffix

2020-02-27 19:03:20,931 ; INFO ; ######################  LOGGING START  #######################

2020-02-27 19:03:20,931 ; INFO ; Blender Version ; (2, 82, 7)

2020-02-27 19:03:20,931 ; INFO ; Bl Build type ; b'Release'

2020-02-27 19:03:20,932 ; INFO ; Bl Build Branch ; b'master'

2020-02-27 19:03:20,932 ; INFO ; Bl Platform ; b'Windows'

2020-02-27 19:03:20,932 ; INFO ; Bl bundled python ver ; 3.7.4 (default, Nov  1 2019, 13:23:36) [MSC v.1916 64 bit (AMD64)]

2020-02-27 19:03:20,932 ; INFO ; cr build type ; release

2020-02-27 19:03:20,932 ; INFO ; cr build branch ; trunk/Blender_addon/2.80/User/Crowdrender r1404

2020-02-27 19:03:20,932 ; INFO ; cr system mode is ; 20

2020-02-27 19:03:20,932 ; INFO ; System architecture ; AMD64

2020-02-27 19:03:20,933 ; INFO ; Computer name ; thor

2020-02-27 19:03:20,933 ; INFO ; Platform details ; Windows-10-10.0.18362-SP0

2020-02-27 19:03:20,933 ; INFO ; OS version ; ('10', '10.0.18362', 'SP0', '')

Crowd Render user_session add-on enabled

2020-02-27 19:03:20,947 ; INFO ; New session, creating directory and files

2020-02-27 19:03:20,954 ; INFO ; CRClient Network interfaces initialised

starting crowdrender...

hash_tree created

top hash changed, new value:  1350811699315527489783871182089

STARTED CROWDRENDER

Blender 2.82 (sub 7) (hash 77d23b0bd76f built 2020-02-13 01:56:46)

Blender 2.82 (sub 7) (hash 77d23b0bd76f built 2020-02-13 01:56:46)

Read prefs: C:\Users\andre\AppData\Roaming\Blender Foundation\Blender\2.82\config\userpref.blend

Read prefs: C:\Users\andre\AppData\Roaming\Blender Foundation\Blender\2.82\config\userpref.blend

found bundled python: C:\Program Files\Blender Foundation\Blender 2.82\2.82\python

found bundled python: C:\Program Files\Blender Foundation\Blender 2.82\2.82\python

Crowd Render Client Interface Process ready

Crowd Render Server Interface Process ready

Traceback (most recent call last):

  File "<string>", line 1, in <module>

  File "C:\Users\andre\AppData\Roaming\Blender Foundation\Blender\2.82\scripts\addons\crowdrender\src\py_3_7\serv_int_start.py", line 68, in <module>

    machine_manager = server_interface.CRMachineManager()

  File "/Users/jamescrowther/Desktop/Crowdrender/cr_compile/releases/multi OS releases/blender_addon/2.80/crowdrender/src/cr/server_interface.py", line 141, in __init__

  File "/Users/jamescrowther/Desktop/Crowdrender/cr_compile/releases/multi OS releases/blender_addon/2.80/crowdrender/src/cr/server_interface.py", line 401, in service_interface_process

  File "/Users/jamescrowther/Desktop/Crowdrender/cr_compile/releases/multi OS releases/blender_addon/2.80/crowdrender/src/cr/server_interface.py", line 573, in process_msgs

  File "C:\Program Files\Blender Foundation\Blender 2.82\2.82\python\lib\json\__init__.py", line 361, in loads

    return cls(**kw).decode(s)

  File "C:\Program Files\Blender Foundation\Blender 2.82\2.82\python\lib\json\decoder.py", line 337, in decode

    obj, end = self.raw_decode(s, idx=_w(s, 0).end())

  File "C:\Program Files\Blender Foundation\Blender 2.82\2.82\python\lib\json\decoder.py", line 355, in raw_decode

    raise JSONDecodeError("Expecting value", s, err.value) from None

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

2020-02-27 19:03:24,731 ; INFO ; CIP is ALIVE

Blender quit

Info: Total files 0 | Changed 0 | Failed 0

What's going wrong here and how can it be fixed?