So you can still submit while multiple photos are uploading?
Yes - or at least when I tried the last time, the upload showed 100%, but the tags were not replaced with the "resize". So maybe the upload was finished, but not the resize? 🤷
Maybe it's a bug with the code that replaces the progress text with the actual filename. https://github.com/NodeBB/nodebb-plugin-composer-default/blob/master/static/lib/composer/uploads.js#L234-L248
So the upload is successful and it lets you submit the post but if the above code fails it won't replace the Upload 100% with the url of the image.
When you reproduce this please check the network tab for the upload request and check if the file was uploaded in your public/uploads folder.
The uploads do not end up in the /uploads/files/ folder.
I'm using the hosted solution of nodeBB, and am of course happy to help debug further!