It's drag/upload images really dies when it's more than a few (on fiber, but that's not the point; in 2022 you need to remember what you were doing when uploading something and keep trying; it simply forgets the image completely and just shows the 'embed image' placeholder without anything in it for the images that 'didn't make it'). It is inconsistent between web, mobile and desktop; for instance, I make a page with 25 images on my desktop, wait for them to fully upload (it always says 100% done in the top but that's a lie; you have to check every photo in the right bottom); if it fails, remove them and doing it again because usually the first 1-2x half of them will just not make it and when done share on web or check on the mobile app, still half are missing even when fully uploaded according to the desktop.
I don't really trust it work reliably for anything but text & links.