Hello @dnakorea!
Tried updating MS-Edge to its chromium based version here. So now I got this: Version 91.0.864.67 (Official build) (64-bit) and...
The upload worked fine in the example!..
There must be something very specific going on. Maybe you're behind a proxy? South Korea (I presume) doesn't have a "great firewall" like China, does it?
Can you clone the
Ext.NET 7 Examples project; build, run and check if, locally, the example turns in the same error?
If the issue happens locally, you should be able to catch the actual issue or exception triggered server-side.
If not, this could be a communication issue with our servers, although I don't really see how it would block upload file requests while the others go fine. Check your browser's developer tools console for exceptions or warnings it may be firing, this could help us understand what's going on.
This may also be an issue related to how ASP.Net Core (or 5) handles file uploads. You don't get the issue if you run google chrome or other browser, do you?
Looking forward to your follow-up!