Please let me know when you find a solution without 1 minute downtime 
We have been using Anvil for 5 years in my company. Our apps interact with uplink scripts to access local resources, with managed servers with ecommerce site, internal wiki, etc, with FedEx and UPS services, with Microsoft SharePoint, with Google maps, etc.
By far most of the down time we had in the past 5 years was due to problems with our internal network. Mostly the internet provider, but also problems with our DNS server, with the 3 VMs the uplinks run on, all kind of routine internal network problems. The very thing we have control over, is what failed us most. Then every single service, including the big guys, have had their fair share of down time. All of them, including Google and Microsoft. Way more than 1 minute.
To be fair, there have been periods where Anvil had more hiccups than desired. Once the email service stopped working, once they deprecated an old domain that I was still using for some http endpoints, and there were a few not-so-smooth upgrades. But also, they once contacted me to tell me that our dedicated server was bogged. I heard from them before I heard from my users. (It was my fault, I quickly fixed the bug and everything was back to normal).
In summary I have 10% of my code on uplinks relying on my own servers, 80% relying on Anvil, 10% relying on other services running on the big guys’ servers. My downtime is 70% on my side, 20% on Anvil and 10% on any of the other parts (the numbers are my feeling, I have no data to show)
A little downtime is inevitable. Not one of the services I use has been 100% reliable.
A little more downtime with Anvil is a price that I am very happy to pay, considering that it has always been growing pain.
I understand you don’t care about growth. You are looking for LTS, I guess you are at the “ain’t broken, don’t fix it” point already. But also the ecommerce and the wiki running on my managed servers should be at that point, and yet they have more downtime than Anvil. (I do have data to show).