Not sure how to reproduce since its a client project I did not build up from the ground. However there is a custom entity and a reference field to the entity inside a node. This custom entity is not clonable and should be disabled from cloning in the "/admin/config/system/entity-clone/cloneable-entities" page.
However, cloning the (parent) node results in a memory limit error already on the entity clone form page (/entity_clone/node/{NID}). Debugging the issue, I notice the ContentEntityCloneFormBase is using the "isClonable()" method but its not respecting the 'cloneable_entities' config. Excluding entity types only works on the 'clone' operation or the 'entity_type.definition.create' Event being fired which according to the comments "The name of the event triggered when a new entity type is created" only fires when a new entity type is created. This of course happens AFTER submitting the form.
Not sure how to reproduce since its a client project I did not build up from the ground. I'm not sure why the custom entity is not clonable.
Add a check for clonable_entities for reference fields in the isClonable() method aswell.
Needs work
2.0
Code
The last submitted patch, 2: 3397218_2.patch, failed testing. View results →
Your if statement seems to be inverted.
Seems more sensible to skip if cloneable entities are empty or if target entity is not present in the array.