traceback: remove(x): x not in container

[oliver-sanders]

Traceback spotted in the wild:

Traceback (most recent call last):    
  File "/lib/python3.9/site-packages/cylc/uiserver/data_store_mgr.py", line 292, in _apply_all_delta                              
    apply_delta(field.name, sub_delta, self.data[w_id])                                                                            
  File "/lib/python3.9/site-packages/cylc/flow/data_store_mgr.py", line 345, in apply_delta                              
    data[FAMILIES][data[key][del_id].family].proxies.remove(del_id)    
ValueError: remove(x): x not in container    
2023-07-18T11:13:57 ERROR    remove(x): x not in container    
Traceback (most recent call last):    
  File "/lib/python3.9/site-packages/cylc/uiserver/data_store_mgr.py", line 292, in _apply_all_delta                              
    apply_delta(field.name, sub_delta, self.data[w_id])    
  File "/lib/python3.9/site-packages/cylc/flow/data_store_mgr.py", line 335, in apply_delta                                        
    data[TASKS][data[key][del_id].task].proxies.remove(del_id)    
ValueError: remove(x): x not in container    

Recipe for reproduction unknown.