I wanted to sort out the country groups in odoo 15 and tragedy struck.

Contacts >> Configuration >> Country group

I removed: SEPA Countries

The group was redefined by me but this did not solve the problem.

When trying to print invoices I get an error:

Traceback (most recent call last):
  File "/odoo/odoo-server/odoo/tools/cache.py", line 85, in lookup
    r = d[key]
  File "/odoo/odoo-server/odoo/tools/func.py", line 71, in wrapper
    return func(self, *args, **kwargs)
  File "/odoo/odoo-server/odoo/tools/lru.py", line 34, in __getitem__
    a = self.d[obj]
KeyError: ('ir.model.data', , 'base.sepa_zone')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/odoo/odoo-server/addons/web/controllers/main.py", line 2020, in report_download
    response = self.report_routes(reportname, docids=docids, converter=converter, context=context)
  File "/odoo/odoo-server/odoo/http.py", line 536, in response_wrap
    response = f(*args, **kw)
  File "/odoo/odoo-server/addons/web/controllers/main.py", line 1949, in report_routes
    pdf = report.with_context(context)._render_qweb_pdf(docids, data=data)[0]
  File "/odoo/odoo-server/addons/account/models/ir_actions_report.py", line 49, in _render_qweb_pdf
    return super()._render_qweb_pdf(res_ids=res_ids, data=data)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_actions_report.py", line 835, in _render_qweb_pdf
    html = self_sudo.with_context(context)._render_qweb_html(res_ids, data=data)[0]
  File "/odoo/odoo-server/odoo/addons/base/models/ir_actions_report.py", line 878, in _render_qweb_html
    data = self._get_rendering_context(docids, data)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_actions_report.py", line 895, in _get_rendering_context
    data.update(report_model._get_report_values(docids, data=data))
  File "/odoo/odoo-server/addons/account/report/account_invoice_report.py", line 166, in _get_report_values
    rslt = super()._get_report_values(docids, data)
  File "/odoo/odoo-server/addons/account/report/account_invoice_report.py", line 148, in _get_report_values
    new_code_url = invoice.generate_qr_code()
  File "/odoo/odoo-server/addons/account/models/account_move.py", line 3416, in generate_qr_code
    if self.partner_bank_id._eligible_for_qr_code(candidate_method, self.partner_id, self.currency_id):
  File "/odoo/odoo-server/addons/account_qr_code_sepa/models/res_bank.py", line 46, in _eligible_for_qr_code
    sepa_country_codes = self.env.ref('base.sepa_zone').country_ids.mapped('code')
  File "/odoo/odoo-server/odoo/api.py", line 578, in ref
    res_model, res_id = self['ir.model.data']._xmlid_to_res_model_res_id(
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 1935, in _xmlid_to_res_model_res_id
    return self._xmlid_lookup(xmlid)[1:3]
  File "", line 2, in _xmlid_lookup
  File "/odoo/odoo-server/odoo/tools/cache.py", line 90, in lookup
    value = d[key] = self.method(*args, **kwargs)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 1928, in _xmlid_lookup
    raise ValueError('External ID not found in the system: %s' % xmlid)
ValueError: External ID not found in the system: base.sepa_zone

The problem occurs both when I want to preview the invoice and when I try to print or save it to PDF.