New customer tag limit
In your Shopify admin, a saved customer now has a limit of 250 tags on the details page. This limit was added to improve the performance of your Shopify store, and applies whether a tag is created manually or automatically by an app.
A customer that already includes more than 250 tags keeps the existing tags, but no more tags can be added to that customer until it has fewer than 250 tags. You can delete tags from the customer details page.
Learn more about managing customers in Shopify from the Shopify Help Center.