Qlik Sense: Browser login prompt after successful virtual proxy authentication

[luigi_b]

I have Qlik Sense April 2019 installed on an external server.

I am able to access the hub through a virtual proxy. But, no matter the type of authentication used,  everytime I access a sheet containing images stored on the Default Content library, a login prompt is shown. If I click "Cancel", none of the image on the sheet and following sheets are shown, whereas images are shown if I authenticate correctly on the prompt.

However, when opening a sheet without images, or when accessing to Qlik throught the default proxy, no prompt is shown and images are shown correctly.

I couldn't find any post related to this issue, apart from a similar one for Qlik June 2019. The issue there is INSIGHT_BOT, which is not present in April 2019 version of Qlik Sense, but I get a similar "302 Authenticate at this location" message and a call to windows login, as shown in the picture below.

This happens on Qlik Sense April 2019 version, but is still present in September 2019 version too. Is this a bug, or can it be solved?

UPDATE: I thought the issue was due to the specific browser used, but it turned out I was wrong. The issue is with the virtual proxy, I still can't see any image on any browser.

UPDATE: anybody able to help? we haven't still figured this out.