Magento 2 tries to load old theme on category pages

Question

I'm using Magento 2.2.3 and after switching from the custom theme (Infortis - Ultimo) to Luma, all category pages are still displaying the Ultimo theme. The rest of the website displays using Luma so the problem is just with category pages. I've uninstalled the custom theme but the category pages still try to load it and give the error...

Exception #0 (LogicException): Unable to load theme by specified key: '6'

'6' is the ID of the old theme. The new theme's ID is '2'. I don't know where in the database there's a reference causing categories to try using the old theme on just category pages.

The order I've tried to do this is...

• Changed theme to Luma in Content > Configuration
• Removed the rows containing umm_ from eav_attribute table (as recommended)
• Removed the custom theme entries from the theme table
• Removed the theme files from app/code & app/design
• Flushed the cache
• Removed var/view_preprocessed (and all the other var/cache files)
• Removed pub/static/frontend/*

I've tried other combinations too but nothing has worked.

Answer 1

I found a fix for this problem. In the database look in the eav_attribute table and get the attribute_id for custom_design in the attribute_code column (e.g. 60). Once you have this number look in the table catalog_category_entity_varchar. Look in attribute_id column for the custom_design value (e.g. 60). All instances of the number had NULL in the value column except one. This was still showing 6. I changed the value to NULL and flushed the Magento cache and now the category pages are using the new theme.

Answer 2

I my case the main category design was assigned to the older theme, I just changed it to the newer theme and without clearing cache on the frontend design displayes as expected.