Self-Solved!
I replaced:
'base' => get_pagenum_link(1) . '%_%',
'format' => 'page/%#%',
'total' => $numpages,
'current' => $paged,
With:
'base' => str_replace( $big, '%#%', esc_url( get_pagenum_link( $big ) ) ),
'format' => '?paged=%#%',
'total' => $numpages,
'current' => $paged,