Post some debug log from 3.4.0-beta3, from https://oil-jenkins.canonical.com/artifacts/6616e90f-975d-4443-9fe7-bbc27fa62bb8/generated/generated/maas/logs-2023-06-15-14.53.09.tgz.
Very close to what we have in #1.

Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 RegionServer,29,::ffff:10.245.222.215: [info] RegionServer connection lost (HOST:IPv6Address(type='TCP', host='::ffff:10.245.222.204', port=5250, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:10.245.222.215', port=45764, flowInfo=0, scopeID=0))
Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 maasserver.ipc: [info] Worker pid:1523454 lost RPC connection to ('tmhdw8', '10.245.222.204', 5250).
Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 RegionServer,30,::ffff:10.245.222.215: [info] RegionServer connection lost (HOST:IPv6Address(type='TCP', host='::ffff:10.245.222.204', port=5250, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:10.245.222.215', port=45766, flowInfo=0, scopeID=0))
Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 maasserver: [error] ################################ Exception: Connection was closed cleanly. ################################
Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 maasserver: [error] Traceback (most recent call last):
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/django/core/handlers/base.py", line 181, in _get_response
Jun 15 14:52:21 sunset sh[1523069]:     response = wrapped_callback(request, *callback_args, **callback_kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 293, in view_atomic_with_post_commit_savepoint
Jun 15 14:52:21 sunset sh[1523069]:     return view_atomic(*args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3.10/contextlib.py", line 79, in inner
Jun 15 14:52:21 sunset sh[1523069]:     return func(*args, **kwds)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 62, in __call__
Jun 15 14:52:21 sunset sh[1523069]:     response = super().__call__(request, *args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/django/views/decorators/vary.py", line 20, in inner_func
Jun 15 14:52:21 sunset sh[1523069]:     response = func(*args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3.10/dist-packages/piston3/resource.py", line 197, in __call__
Jun 15 14:52:21 sunset sh[1523069]:     result = self.error_handler(e, request, meth, em_format)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3.10/dist-packages/piston3/resource.py", line 195, in __call__
Jun 15 14:52:21 sunset sh[1523069]:     result = meth(request, *args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 371, in dispatch
Jun 15 14:52:21 sunset sh[1523069]:     return function(self, request, *args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/api/support.py", line 217, in wrapper
Jun 15 14:52:21 sunset sh[1523069]:     return func(self, request, *args, **kwargs)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/api/pods.py", line 346, in compose
Jun 15 14:52:21 sunset sh[1523069]:     machine = form.compose()
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/maasserver/forms/pods.py", line 741, in compose
Jun 15 14:52:21 sunset sh[1523069]:     ).wait(timeout)
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/crochet/_eventloop.py", line 198, in wait
Jun 15 14:52:21 sunset sh[1523069]:     result.raiseException()
Jun 15 14:52:21 sunset sh[1523069]:   File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 475, in raiseException
Jun 15 14:52:21 sunset sh[1523069]:     raise self.value.with_traceback(self.tb)
Jun 15 14:52:21 sunset sh[1523069]: twisted.internet.error.ConnectionDone: Connection was closed cleanly.
Jun 15 14:52:21 sunset sh[1523069]: 2023-06-15 14:52:21 maasserver.ipc: [info] Worker pid:1523454 lost RPC connection to ('tmhdw8', '10.245.222.204', 5250).