"A non-existent config entity name returned by FieldStorageConfigInterface::getBundles()" errors in watchdog

After migrating from 7 to 9, I'm getting a lot of these errors in watchdog, from views.

A non-existent config entity name returned by FieldStorageConfigInterface::getBundles(): entity type: paragraph, bundle: iframe, field name: field_url

Things I've tried:

• Checking paragraph bundles(types): there are only two, the iframe one does not exist (I don't need it in the new site).

• drush cr

• drush config:export then grepping the files for iframe: it only exists in media.settings.yml as iframe_domain: '' - not relevant

• grepping the config files for field_url - not found.

• maybe there's some old content referencing the iframe bundle? select distinct type from paragraphs_item; only shows the new bundle names. Same for paragraphs_item_field_data

• show tables like "%field_url%"; This does reveal two tables: paragraph__field_url and paragraph_revision__field_url - I would have expected these to be deleted. They are both empty though.

• show tables like "%iframe%"; - none.

• I've been through all the views - but these are all the default D9 ones, plus a few I've added myself for the new site, which do not have anything to do with paragraph bundles.

• I checked the fields-used-in-views report - field_url is not there.

• I checked the fields list report. field_url is there, and weirdly, it says the entity type is paragraph but then it says:

  Text (plain) (module: core)

• I tried re-creating a paragraph type called iframe and then deleting it.

• I tried to add a field called url, but it is forbidden because that machine name already exists.

I'm stumped as to how to get rid of these errors/notices.

Update

I found some config yml files that related to this URL field. I deleted those and did a config import, which seemed to clear the problem for that field, but opened it up for other fields.

It's now complaining about entity type: paragraph, bundle: grid_item_node_list, field name: field_text

However I can't use the same deletion approach for that field as it is in use for new content (on different paragraph bundles).

In exported config, no files contain grid_item_node_list and no files have that in their name. Yet when I grep the database I find :

cache_config.cid contains 2:

• field.field.paragraph.grid_item_node_list.field_page_ref
• field.field.paragraph.grid_item_node_list.field_text

And cache_default.data also contains grid_item_node_list as does cache_discovery.data and key_value.value (for name: paragraph).

I don't understand why (a) these config aren't exported, and (b) why the cache-related ones aren't cleared on drush cr.