@Grisu – Thank you for letting me know, I have checked also and found the same problem, I have adjusted the CSS cache and seems to work for me now, when I select refresh.
Let us know if this also now works for yourself 
Issue is now that for logged in forum members, page loads maybe even slower, or I can disable the new posts banner which would then speed up forum members forum usage when moving between different pages.
Never an easy choice is there 
.’. For a test I will disable New Post Banner for a couple of days and see if that makes forum page load quicker and see how Forum members like the page load speed gains vs loss on New Post Banner markings on Forums that have not been viewed.
In a completely sane world, madness is the only freedom (J.G.Ballard).
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