I have seen a few instances where a certain combination of launch method and browser leads to query parameters being dropped for no apparent reason, specifically I've seen this happen once or twice with Internet Explorer 11 and the Web Player launch method. You can either use a different browser or launch method, and it should work.
However, if it happens across different browsers something else is amiss, i.e., you have some kind of configuration error in your setup. Note that query parameters coming into the launch page will only be preserved if the URL to redirect to is specified via the web script wizard. If your Inquisit *scripts* override that finish URL via by setting defaults.finishpage, all incoming query parameters will be discarded.
If you want to provide the link to the respective web experiment, I'll be happy to give the configuration a look and see if I can spot any issues.