I've found an older version of the theme you are using on my test servers and I took a quick look. I'm not sure if you are using the same version, but I have found the problem.
Open up the wp-content\themes\wp_oswad_market\framework\functions\pagination.php file, and look for this line (line 86 on my screen):
elseif(strpos($pageLink,'?') >= 0 && strpos($pageLink,'&') === false)
and change that to:
elseif(strpos($pageLink,'?') >= 0)
And that should solve the problem hopefully.Best,
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