Special characters in Shopify tags
Special characters in tags are not handled very well by Shopify as a result sometimes the app fails to add a tag when a similar tag is already present on the entity (order, customer, product). In this case, if the workflow is triggered again for that entity, it will try to add the tag again resulting in unnecessary tag consumption.
There are some tags that are completely identical except for special characters (spaces instead of commas/hyphens). For example, If "color grey" is already there on a product, the app fails to add "color-grey" due to Shopify's limitations in dealing with special characters.
For context, If you try adding a "color-grey" tag, it will replace the tag instead, and Auto Tags don't remove any tag until it is specifically configured to do so.
To make tags work best for you and your business and to avoid such events:
Use only ordinary letters, numbers, and the hyphen (-) in your tags. Avoid accented characters and other symbols.
Although you can create tags that use some special characters, they might not work as you expect in searches or as conditions in automated collections. Special characters in tags are either ignored or are treated as being the same.
For example, Suppose you have a condition for an automated collection of Product tag is equal to red-new. All products that have the following tags are also included in the collection: red_new, red+new, red&new simply because Shopify doesn't differentiate between these special characters in tags.