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.
That fixed it for me, too! Thanks!