images not resizing anymore

I did a wordpress website for a gallery and they recently decided to change of host solution (they kept the same host but downgraded from a dedicated server to a shared system)

the website was working ok but now it seems that no thumbnail nor medium and large versions are generated anymore when a new picture is uploaded

which is really problematic for the design…

what can I do to fix that issue ?

I also got the following errors when I go to the Media Library

Warning: explode() expects parameter 2 to be string, array given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2390

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399

Warning: in_array() expects parameter 2 to be array, null given in /home/gllrnin5/public_html/gn5/wp-includes/query.php on line 2399