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The only way to fix this issue only disable the SEF, I am not sure why this issue happens with your SEF, but I am afraid this is caused by 3rd party plugin since I see lot of plugins on your site
If you wanna curious with this, I suggest you install new Joomla and Jomsocial, plus set SEF enable, and try this issue there.
Which plugin??
I'm not install any plugin after the jomsocial update. Before the jomsocial update everything were working right.
We need a solution. Is very urgent.