This is a long-standing showstopper bug, with many reports over the past years.
The problem is mostly related to network speed and file size (not to device, browser or OS) so you are more likely to see it on a phone, but I can demonstrate it on iOS, Windows, Mac, and with a variety of browsers (Chrome, Edge, Safari Desktop or mobile)
WebFileUploader is unfortunately even more broken in Web2:
Critical Bugs
- <https://xojo.com/issue/61753> WebFileUploader: UploadFinished fails to fire (Of historical note, I reported this nearly six years ago back in 2014: <https://xojo.com/issue/36686> )
- <https://xojo.com/issue/62073> WebFileUploader does not allow multiple files
Other issues:
- <https://xojo.com/issue/61741> WebFileUploader performance issues
- <https://xojo.com/issue/61692> WebFileUploader - clicking Cancel on the select file dialog removes the file without the FileRemoved event (this seems to be a Chrome only bug)
- <https://xojo.com/issue/62074> WebFileUploader.UploadFinished : WebUploadedFile.mimeType is incorrect
Here’s hoping they can get it working soon.