Lovelace unusable following change to entities, help me recover?

I’ve had a long-stable HA 0.92.2 as the platform for my home automation and alarm, using Konnected. Recently I discovered a problem with konnected, and had to change the wiring between two terminals, resulting in the need to change an element name. It seems I did something wrong when changing the element name, and as a result Lovelace is unable to load. I get only:

Unknown Error
Reload Lovelace

in the log:

2020-05-25 13:45:37 ERROR (MainThread) [homeassistant.components.websocket_api.http.connection.2943626736] Error handling message: Unknown error
Traceback (most recent call last):
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/websocket_api/decorators.py", line 17, in _handle_async_response
    await func(hass, connection, msg)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/lovelace/__init__.py", line 178, in send_with_error_handling
    result = await func(hass, connection, msg)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/lovelace/__init__.py", line 199, in websocket_lovelace_config
    return await hass.data[DOMAIN].async_load(msg['force'])
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/lovelace/__init__.py", line 102, in async_load
    await self._load()
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/lovelace/__init__.py", line 120, in _load
    data = await self._store.async_load()
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/storage.py", line 81, in async_load
    return await self._load_task
  File "/usr/lib/python3.5/asyncio/futures.py", line 382, in __iter__
    return self.result()  # May raise too.
  File "/usr/lib/python3.5/asyncio/futures.py", line 285, in result
    raise CancelledError
concurrent.futures._base.CancelledError

I found another thread with what looks like the same problem:

https://community.home-assistant.io/t/help-amateur-here-cant-access-frontend/110480

This points to “a syntax problem in my storage/core.entity_registry”. I’ve looked and can’t find anything suspicious there.

Another poster recommended removing core.entity_registry, core.device_registry and core.config_entries, which I tried. That didn’t help either.

By stripping down my groups.yaml file to bare minimum and restarting I can get HA to show me Lovelace with just the alarm panel, but then if I reload the browser it goes back to the error message.

I realize I’m way behind in upgrading but the system was stable and I didn’t want to introduce any risk. Now it seems I’m hosed. Can anyone recommend any way out of this?