It appears to be a browser related issue as teh system is working fine with users creating designs. For a double check please follow the points below:
DesignBold is completely compatible with all the browsers (Chrome, Firefox, Mozilla, Safari).
The only interfering point might be the cache and the extensions that you have installed in the browser being used. Also, Ad blockers interfere with the script loading.
So, just to rule out any browser related issue, can you clear your system cache, remove the extensions (or use the incognito mode of the browser), deactivate the Ad Blockers and try again.
You may also, install a fresh browser like Opera (without any history and extensions) and try editing the design.
Do keep us updated with your progress.