It means you’ve Magento 1 theme configurations in the migrated database.
You can fix this problem by finding “default/theme327k” under
cms_page table (column
custom_theme) in the database and remove the column entry to fix this problem.
Run below query in the database to find the rows having M1 theme selected.
SELECT * FROM `cms_page` WHERE `custom_theme` LIKE '%default/theme327k%'
Hope it helps!!!