I have encountered a very perplexing issue.

It came to my attention because Google Ad conversion tracking is not working on the site. Whilst investigating that, we discovered the following:

Any time there is the string gclid in the query-string (e.g., https://our-domain.com/reviews/?test=test&gclid=test the page will redirect to the same URL, minus the query-string (e.g., “https://our-domain.com/reviews/). It can appear anywhere in the query-string, and this redirection will occur. For example, https://our-domain.com/page-1/?test=test&something-else=45&textgclidtext=444will redirect tohttps://our-domain.com/page-1/`

It occurs even when all plug-ins are disabled.

It occurs with any theme I activate.

I see nothing in the .htaccess that would cause this. What’s more, this is a Multi-site installation, and the other 4 sites don’t have this issue (yet they all share the same root folder, obviously, so they share the same .htaccess file).

My question is, what else within WordPress could I look into as part of troubleshooting this issue? I’ve covered all the things I can think of (theme, plug-ins, .htaccess) and none of them appear to be the source of this unusual redirect.