This is caused by the auto optimize plugin you have added to the site. Try disabling it and clear its cache (if it has one) and see if things work normally.
nah, probably not, as the problem remains when adding ?ao_noptimize=1 to the URL which disables AO for that request.
Error on console;
20:35:23.967 ReferenceError: cl_settings is not defined
<anonymous> rsm-min-js-8479219c444729aa3ee68a070ab7432d.js:2
n.Callbacks/i() rsm-min-js-h8479219c444729aa3ee68a070ab7432d.js:1
n.Callbacks/j.fireWith() rsm-min-js-h8479219c444729aa3ee68a070ab7432d.js:1
.ready() rsm-min-js-h8479219c444729aa3ee68a070ab7432d.js:1
K() rsm-min-js-h8479219c444729aa3ee68a070ab7432d.js:1
1 rsm-min-js-8479219c444729aa3ee68a070ab7432d.js:2:92
frank (nosy ao dev)