When updating to a new version, you can copy current settings from one version of the theme to another. Sometimes, a page template is not transferred successfully causing a 404 error on the Home, Collection, or Product pages.
To resolve the issue, you can manually copy the affected page(s).
How to Manually Copy Pages
STEP 1
In Shopify Admin, click on Online Store > Themes.
STEP 2
Click on the three-dot button of the desired theme.
STEP 3
Click on Edit Code to open the code editor.
STEP 4
On the Templates folder, click Add a new template.
STEP 5
Select the template to create as a JSON format and save it (Please note that the file name will not appear in these cases).
Each page has a different template name, therefore select the one where the 404 error appears.
Home page - index
Collection page - collection
Product page - product
You can copy the file from your older version and paste it into the new theme or you can reset your page manually from the theme editor.
