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I think you may need to check your signature (at Special:Preferences). It appears that there is <nowiki> in there without a matching </nowiki>. Generally it will be invisible with no apparent effect (explaining why you haven't noticed it), but there can be a page breaking interaction when someone else makes a comment including a <nowiki> </nowiki> pair. You should probably just remove the <nowiki> in your signature, but you could add a matching </nowiki> somewhere after it if you actually need it.