Intermittend attachment upload issue: smf_fileupload.js

[@rjen]

SMF version: 2.1.2
PHP version: 7.4.29

Intermittend issue reported by users on my forum.
I just managed to reproduce it once, now it works again.

So far reported when uploading attachments with Firefox and from Iphone:

After adding an attachment file, pressing [UPLOAD] results in a 'hung' upload: the green progress bar does not finish and the [INSERT] button never shows.

See example:

You cannot view this attachment.

In the inspector I see tow errors with script: smf_fileupload.js

See errors:

You cannot view this attachment.

The problem is not consistent, now it works again...
Any clue what is going on?

[Steve]

My first inclination would be to try a different browser and type of phone and see if you could still reproduce it.

Other than that, I'll back out and let the coding geniuses take over.

[@rjen]

Tried that and so far I have only been able to reproduce it once on Firefox, but now I also have reports that the same occurs on Chrome. Again intermittently...