Final answer:
The JSON formatted string from a Liquid template containing HTML tags is invalid for parsing in JavaScript. The remedy is to eliminate or escape those HTML tags to maintain a valid JSON structure.
Step-by-step explanation:
The likely cause of the issue where a JSON formatted string returned from an alternate Liquid template contains HTML tags and is not recognized as valid JSON by a JavaScript function is option C) HTML tags in the JSON string. In JSON, data should be in a format that is easy for machines to parse and generate, and HTML tags are not valid within the JSON structure. To resolve this, ensure that the output from the Liquid template is properly encoded and does not contain HTML tags, or if it does, these tags need to be effectively escaped or removed from the data before it is parsed by the JavaScript function.