My screen flashes
Your screen is flashing like crazy when you log into your PC/browser via Gumb-WEB? You've also deleted the caches, cookies, etc.?
The main reason for this is that your "business notebook" is blocked by an "ad blocker". You can't fix this because your employer or their IT usually disables these settings and doesn't allow you to change them.
It will work if you use a private access/browser instead of a business PC/browser.
The contact form can be used if you need further assistance or have additional questions.