Issues like this can be difficult to track down at times. You’ve started down the correct path by narrowing the scope of the issue down to those 3 widgets.
If there is any additional information such as the name of the theme and the widgets you’ve found to cause the issue that would be helpful. Of course, if we’re talking about a custom theme or widgets then providing source code examples will be your best bet.
A couple of things to try:
1) While debugging is turned on check your XHR / AJAX console for requests occurring in the background that might be failing.
2) Check your Javascript console for any frontend errors that might be preventing the page from finishing.
3) Check the source code of the 3 offending widgets to see what they might have in common such as similar fields, script references or hooks.
FWIW, I would have preferred to add this information as a comment but my REP isn’t high enough yet. I hope this helps.