The issue can be verified with browser cache disabled (Test Case is: new initial donation from client) and throttling using either Chrome Developer Throttling Tools (Slow 3G and sometimes Fast 3G as well) or third party software (NetLimiter with download settings set below 100-120 KB/s)
Given the following simple example below and the conditions mentioned above:
Clicking the button results in a popup that has the loading message and no way to close it. It's basically stuck in loading.
With browser cache enabled, the second time the page is refreshed it loads without issues.
With bandwidth download above 120 KB/s there are no issues whatsoever.
I've received several reports of this happening from various users and need a fix for this as quickly as possible as it is affecting our users tremendously!
We are seeing the same issue. It seems to be some sort of timing issue with slow connections (or page loads from people who have never loaded other site assets). Thus far we haven't found an acceptable workaround but I'm adding this +1 to see if it will spark any replies and to add to the list of folks seeing the issue.