Can't save an item (Error: Document has been modified after you have opened it)

Context information (for bug reports)

Output of bench version

erpnext 13.5.0
frappe 13.5.0
woocommerceconnector 1.6.0 (aadhilpm fork)

Problematic code

        for variant in variant_list:
            erp_varient_item = frappe.get_doc("Item", variant["item_name"])
            if (
                erp_varient_item.woocommerce_product_id
            ):  # varient exist in woocommerce let's update only
                r = put_request(
                    "products/{0}/variations/{1}".format(
                        erp_item.woocommerce_product_id,
                        erp_varient_item.woocommerce_product_id,
                    ),
                    variant,
                )
            else:
                woocommerce_variant = post_request(
                    "products/{0}/variations".format(erp_item.woocommerce_product_id),
                    variant,
                )

                erp_varient_item.woocommerce_product_id = woocommerce_variant.get("id")
                erp_varient_item.woocommerce_variant_id = woocommerce_variant.get("id")
                erp_varient_item.save() #<--- this is line 739

Observed result

An error is thrown when saving the item on line 739. I believe this is only a problem in v13 as people are using this branch in v12 without problems.

Expected result

The item is saved without any exceptions.

Stacktrace / full error message

Traceback (most recent call last):
  File "/home/erp/frappe-bench/apps/woocommerceconnector/woocommerceconnector/sync_products.py", line 535, in sync_erpnext_items
    sync_item_with_woocommerce(
  File "/home/erp/frappe-bench/apps/woocommerceconnector/woocommerceconnector/sync_products.py", line 739, in sync_item_with_woocommerce
    erp_varient_item.save()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 285, in save
    return self._save(*args, **kwargs)
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 314, in _save
    self.check_if_latest()
  File "/home/erp/frappe-bench/apps/frappe/frappe/model/document.py", line 725, in check_if_latest
    frappe.msgprint(_("Error: Document has been modified after you have opened it") \
  File "/home/erp/frappe-bench/apps/frappe/frappe/__init__.py", line 411, in msgprint
    _raise_exception()
  File "/home/erp/frappe-bench/apps/frappe/frappe/__init__.py", line 365, in _raise_exception
    raise raise_exception(msg)
frappe.exceptions.TimestampMismatchError: Error: Document has been modified after you have opened it (2021-06-15 20:22:22.159850, 2021-06-16 20:06:02.811495). Please refresh to get the latest document.

Additional information

ubuntu 20.04 with production settings

frappe / erpnext

Can't save an item (Error: Document has been modified after you have opened it) #26084