I'm not sure how long it took, but for a while the instance had crashed. For some reason the Lemmy photo upload service took up 150GB of free space and hence the server crashed because of it. I'm not sure about the possibility of recurrence as I don't know the exact reason.
For this reason, you can follow our Mastodon account, which I have just opened, to follow or report possible crashes.
I don't think we should rely on Lemmy's uploading at all. The whole federation is very unstable, the last thing it needs is to have gigabytes of porn sent to it.
There's no clear replacement for Imgur yet but there are viable alternatives.
I have been using Free Image Host for my own, at least for now.
Catbox is simple but unfortunately unreliable as well. Had it go down a few times out of nowhere.
Both of those are very compatible with Sharex.
IMGPile is another choice, and it also has gallery support IIRC though only if you register.