urlparam stopped working

Suddenly urlparam has stopped working. Don’t know whether it was an update to WordPress or another plugin. So I cloned the working live site to a development platform running the same version of wordpress and all plugins. and user data. Unexplicably urlparam works fine on this development site.. So disabled all unnecessary plugins on the live site but the problem remained. Downgraded WordPress from 6.22 to 6.11 in steps but still no joy. If i deactivate urlparam the page displayed the shortcodes as you would expect, so the parameters are being passed to the page correctly – urlparam just ignores them and outputs nothing. How to debug this? Any pointers will be appectiated.

Thanks,

Spindles7