Missing bundle property on entity of type node Error when unique validation rule applied.

I have a database of several thousand nodes of a product content type. They were imported using Feeds Importer and I had to do the process several times. I used the module Delete All to remove all of the imported nodes between imports.

I have found a few products (not all) that cannot be updated if unique validation rules are applied to a couple of fields for the content type.

When saving an updated node I get this error message:

Error messageEntityMalformedException: Missing bundle property on entity of type node. in entity_extract_ids() (line 7697 of /httpdocs/includes/common.inc).
The website encountered an unexpected error. Please try again later.

Again this isn't happening for all nodes of the content type, only some. Caches have been cleared.

I have tried various options in the validation rule but they all produce the same result. If I delete the unique rule the problem nodes can be udpated without error.

When the error occurs I cannot remove the node from the database either. I get the same error message.

I tried manually deleting the node from MySQL and removing associated entries in all of the fields, revision, and node tables. After clearing the cache several times I dumped the database and did a search on the unique values in the SQL file and found references to the field values I had deleted in some of the cache tables including:

cache_bootstrap
cache_field
cache_form

I'm not sure what else to check or try at this point. Validating these fields as unique is important to the site.