Strange lag on this website/ bad connection

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I've been experiencing problems with this site in the last few days when I'm in my WLAN at home. I often have extreme lag on this forum and pages load incredibly slowly ... it usually happens at daytime, roughly between 9 a.m. and 9 p.m.
Every other site works fine, so it can't be a problem with my connection per se. This site also seems to work fine when I access it on my mobile phone (with mobile data), so it can't be that the site is slow per se.
Does anyone have an idea what the problem might be? Some IP conflict or something? Any ideas what I could do about it?

 

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Since around 22.15 the forum has been back to normal again (the same happened yesterday) ... and it will probably start lagging again for me next morning. It's really strange.

 

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It has gone back to being laggy again after working decently earlier this morning ...
There seems to be a window from around 10 a.m. to 10 p.m. in which the forum is horribly slow for me

 

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Now it's working ...

 

[rothbard]

That's strange, I haven't noticed a lag. When the connection is slow for your, how long does it take for the forum to load?

 

[Bitmap]

That's strange, I haven't noticed a lag. When the connection is slow for your, how long does it take for the forum to load?

It feels like being on ISDN.
Today, it has been working well so far, though.