How to reproduce (it happens in Chrome, haven't tested other browsers):

1. Login in hq moodle site.
2. While in dashboard, click the message icon next to a user in the online users block. You'll be sent to the message index page.
3. Click Back in the browser. Once the dashboard is loaded again, an invalidresponse error modal appears.

I inspected the network requests, it seems to be related with user tours:

args: {

    tourid: "4",

    context: 301,

    pageurl: "https://HQMOODLESITE/my/"

}

index: 0

methodname: "tool_usertours_fetch_and_start_tour"