Data Import Error - Item attribute value already exists - The value is already assigned to an exisiting Item

I am trying to migrate my data from V10 to V12 using data import tool , as i failed to do restore using the “bench restore”.

I exported the items from V10 to an excel.
i used the import tool in V12
next i started to import the items. some items where imported without any problem
other items will give me " The value 22 is already assigned to an exisiting Item SW-UTLT-22" yet this is the first time to import this item to the system.
after this failure, it keep giving me this error.
the strangest thing , if i search the item “SW-UTLT-22” , it will show in the search list. if i select the item from the search list , it will give me item is not found ??

Traceback (most recent call last):
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/core/doctype/data_import/”, line 410, in upload
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 230, in insert
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 895, in run_before_save_methods
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 794, in run_method
out = Document.hook(fn)(self, *args, **kwargs)
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 1065, in composer
return composed(self, method, *args, **kwargs)
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 1048, in runner
add_to_return_value(self, fn(self, *args, **kwargs))
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/model/”, line 788, in
fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs)
File “/home/ttcdist/frappe-bench/apps/erpnext/erpnext/stock/doctype/item/”, line 115, in validate
File “/home/ttcdist/frappe-bench/apps/erpnext/erpnext/stock/doctype/item/”, line 841, in validate_variant_attributes
validate_item_variant_attributes(self, args)
File “/home/ttcdist/frappe-bench/apps/erpnext/erpnext/controllers/”, line 73, in validate_item_variant_attributes
validate_item_attribute_value(attributes_list, attribute, value,
File “/home/ttcdist/frappe-bench/apps/erpnext/erpnext/controllers/”, line 102, in validate_item_attribute_value
attribute_value, attribute, item), InvalidItemAttributeValueError, title=_(‘Rename Not Allowed’))
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/”, line 377, in throw
msgprint(msg, raise_exception=exc, title=title, indicator=‘red’, is_minimizable=is_minimizable)
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/”, line 356, in msgprint
File “/home/ttcdist/frappe-bench/apps/frappe/frappe/”, line 316, in _raise_exception
raise raise_exception(msg)
erpnext.controllers.item_variant.InvalidItemAttributeValueError: The value 22 is already assigned to an exisiting Item SW-UTLT-22.