I'm self-hosting and it has been ridiculously smooth coupled with Voyager as my mobile app. Now I understand that a single user instance is a lot easier to handle than a multi-user one so I naturally don't have any experience or opinion on how Lemmy instances scale with users in terms of stability.
Right now, another bug has manifested itself. Your message is shown in the "Replies" tab in Jerboa's inbox, but it is not visible in the comments of the message thread.
For a few months, I couldn't log into this instance through apps.
Yesterday, the lemmy.today instance stopped sending posts and messages to the Lemmy network. I only found out about it when I logged in through another instance in asklemmy and saw that my post wasn't in the community.
This happened to me when my language settings weren't set. You can't even access them in jerboa, log in with a browser and check if English is selected besides default. And whatever else you wish to see.