Simply detele the string after customize.php,
the “?return= ..” part, then you should be able to run the page.
I am also on HostGator, which the wordpress supporters might not know why.
I am encountering similiar problem, and I found the string starting with “?return=” causes the problem.
Clearly,
/wp-admin/customize.php?return=https%3A%2F%2Fwordpress.com%2Fdesign%2F…%3A%3A…
might 403, while
/wp-admin/customize.php
works fine.
It doesn’t harm my using but is just a little bit annoying for doing so everytime.
