This is a bug caused by some "under the hood" changes from 8.3. We're tracking it internally at a fairly high priority - it'll likely be fixed in 8.3.4 or shortly therafter.
In the meantime, you could try this as a workaround:
from com.inductiveautomation.ignition.common.alarming.query import AlarmQueryResultImpl
def datasetFromAlarms(alarms, historical=False):
inner = AlarmQueryResultImpl(historical) # pass True if using queryJournal
inner.extend(alarms)
return inner.dataset
alarms = system.alarm.queryStatus(state=["ActiveUnacked", "ActiveAcked"])
ds = datasetFromAlarms(alarms)