Instances page is empty, throws validation error

Hello,

after adding a couple of instances, the instances UI suddenly blanked out and everytime I try to open it, I get a "Validation Error" (contents below). All configs of my instances disappeared (the instances are still running, though).

Contents of the validation error:

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/middlewared/api/base/server/ws_handler/rpc.py", line 310, in process_method_call
result = await method.call(app, params)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/middlewared/api/base/server/method.py", line 40, in call
result = await self.middleware.call_with_audit(self.name, self.serviceobj, methodobj, params, app)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 877, in call_with_audit
result = await self._call(method, serviceobj, methodobj, params, app=app,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/middlewared/main.py", line 686, in _call
return await methodobj(*prepared_call.args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/middlewared/schema/processor.py", line 174, in nf
return await func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/middlewared/plugins/virt/instance.py", line 133, in query
'netmask': int(address['netmask']),
^^^^^^^^^^^^^^^^^^^^^^^
ValueError: invalid literal for int() with base 10: ''

Session ID: 3e7c4c47-9282-0047-db1b-b35568b8785c