don’t cache forum pages

Hi,
when a user logs into my forum on https://www.apis.de/forum and then clicks on a post within the forum (i.e. https://www.apis.de/forum/…….), it shows that they are logged out (pressing F5 fixes this).
I have set in the “Exclude” settings: “IF REQUEST URI Contains forum”
But this does not seem to do the trick. Any ideas?

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