For me it gets hung on the processing wheel indefinitely, doesnt even return a fail state. If i close the browser tab and return to draft or even if i make a new post in a different thread to uload different images, it will show the processing image wheel where the select photo button usually is.
I have to close the actual browser app to get it to go away. This happens five or ten times in a row wether its one image or five, and its always the same images when it succeeds, so nothing to do with the images themselves.
Ive also tried different non-chrome based web browsers and it’s the same error and issue, which is what had me thinking its either an issue with my old broken phone that cant suspend apps (or receive a notification with out crashing an app) or something to do with Meta Discourse and modified android OS not interacting well.
I also tried viewing the site in desktop mode on the phone browser since I don’t have this issue when uploading from PC.
What I have noticed is that two/three photo’s seem to have a higher success rate than trying 1 photo, and one or four/five photos basically never works. Just gets hung on the processing buffer wheel loop.
Its also really hard to Google the error because whenever you type “discourse forum bug image upload stuck on processing” the search results give people having discourse, about forum bugs, and not Discourse branded forums.
If i simplify the search, i get people who operate discourse forums who are having issues getting their custom theme images to upload to their ftp and display correctly.
No, google, no, I need bug reports and solutions on the user’s end, not the operators 
The final solution of buying a new phone that doesnt have broken RAM also did not proove fruitful.
But hey, i have a phone that can multitask again, had to happen sooner or later 