Annoying red triangle with an exclamation mark in system tray

I had a read through some similar topics to this problem but none of them actually figured out how to solve this. The topics are still open without "niked" answers.

Does anyone know what can I do given that I'm using mirror for the UK (I tried different ones too), system says it's up to date and when I run 'apt-get update / upgrade' nothing really changes. No error messages. Simply nothing. Nada.

What can I do ?

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