Today after updating my site to latest WordPress version 4.5. i came along this issue. My customizer preview init is totally blank with no section and panel. Along with i got this error on console
Uncaught TypeError: data.defaultValue.substring is not a function
How i solved this issue?
- First I deactivated all plugin installed on a site to see if plugin is creating issue.
- Then I dequeue all the scripts from functions.php as well from customizer file where theme had added for creating customizer setting. To make sure which file is creating conflict i tried by removing file sequentially that is added on functions.php
- After I found that the file where customizer setting for control,setting, panel and section is causing the problem.
- Then to know if setting id is creating conflict i tried by changing all section id to different value then tracking one by one.
- Finally I found setting id “widget_titles” is creating problems and changed to some XXXX id which solve the issue
After debugging for 3 hour finally i found the solution of the problems.
Conclusion: Always name options id,setting id and , functions prefixing with theme or plugin slug. It will prevents your id conflicting to other third party or WordPress core itself.
Thanks
Sushil Adhikari
Sushil Adhikari 
I have same error in my wordpress website http://www.fitartech.com. I am not able to sort out. Can you explain your conclusion. Please help me out. Thanks.
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Hi Vaibhav Kumar,
I just gone through your site and found that there is no any js conflict. You just check if your customizer id is conflicting to default WordPress options id.
To know which options is making conflict , first try by deactivating all section manaually. After you detect the section then go for disabling every customizer setting.
In this way you can find conflicting id and then change that id to any other id prefixing with your theme or plugin domain.
Note: Be sure you had include customizer file on functions.php.
Let me know how it will goes.
Thanks
Sushil Adhikari
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