Failed uploads stay in queue and never try again

Expected behaviour

If the server is temporarily unable to accept an upload (for example, permissions or file-size restrictions) of one or more files/images, a user should be able to manually trigger a retry for queued files.

Actual behaviour

During a server migration last month, 140 images/videos got stuck in queue. Each queue element looks like:

The circle at right has a square "stop" button but that only cancels the transfer of that item, permanently. There is no other option, so I leave the queue in place hoping for a fix.

Steps to reproduce

1. Install an nginx reverse-proxy in front of Nextcloud server
2. Set the client-body-buffer-size / proxy-body-size nginx parameters to a value smaller than the images you have on your phone, say 100K
3. Take a few pictures
4. Start Nextcloud IOS app and look for the 413 errors to show up
5. Adjust the nginx parameters back to a normal level (unlimited, or >=1G)
6. Go back into this IOS app and see the queued pictures remain stuck

iOS version

12.1.1

App version

2.22.7.4

Server configuration

16GB RAM 1TB SSD gigE Ethernet

Operating system:
Ubuntu 18.04

Web server:
nginx from quay.io kubernetes plus the apache2 built into docker image

Database:
Internal sqlite

PHP version:
7.2.13 built into official image

Nextcloud version: (see Nextcloud admin page)
NextCloud 15.0.0 official docker image, 4GB allocated

Start by locating the iOS upload queue that retains failed 413, permission, and server-error items, then trace the existing stop/cancel control. Reproduce the nginx size-limit failure and verify that, after the limit is raised, a user can manually retry queued files without losing them.