I'm attempting to create a new unlocked manage package version and I'm getting an unexpected issue where the fields on my custom object that are part of the package can't be found. Previously I have never had this issue on this same package.

I'm using a scratch org for development
I'm using sfdx-cli v7.173.0

I have created a permission set (and assigned to the scratch org user) that includes the object and FLS permissions to the fields, and yet I'm getting issues like this (one for each field on the custom object)
No such column 'Class__c' on entity 'Exception_Log__c'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names.

I've also added the FLS to the Admin profile, but that doensn't help and this should work with a permission set anyway.

Am I missing something obvious?