I had nine active plugins and deactivate them one by one to try and find one that was an issue, but even after I deactivate ALL plugins, the Customize screen never loaded.
Here is a list of the plugins which were originally active:
Easy Forms for MailChimp from YIKES
Insert Headers and Footers from WPBeginner
Jetpack by WordPress.com from Automattic
Limit login attempts from Johan Eenfeldt
Quick Feature Images from Martin Stehle
ShareThis from ShareThis Team
SumoMe from SumoMe
TinyMCE Advanced from Andrew Ozz
Tumblr Importer from wordpressdotorg
Here is a screen capture of the Customize page.
https://www.dropbox.com/s/hwvw8cxr3f20rc8/jomsom-bys01.png?dl=0
There are no errors — nothing loads. All the other Admin areas of the WP site work and load correctly.
I then tried switching to a different theme and entered the Customize area and it loaded correctly and as expected.
Then I deleted the Jomsom theme from WP and downloaded the theme again from your website and tried re-installing it per your instructions of Dashboard=> Appearance=> Themes=> Add New (which IS the way I originally installed it).
Unfortunately, now with a fresh install, zero active plugins, etc. I am getting the exact same result. Everything works, but I can’t get anything to load on the Customize screen beyond what appears in the screenshot linked above.
What else can I try?
NOTE: In case this helps…
I am using a Toshiba laptop running Windows 8.
I’ve tried loading the Customize page in the latest versions of Chrome and Firefox.