Recent issues with NORA availability have been caused by the high number of online users reaching over 2400 at any time. Unfortunately the current implementation and the existing free Heroku instance can not handle this kind of load.
There is a new version (Smart NORA) released that is backed by Firebase and is able to handle tens of thousands of concurrent users without a problem.
Being a big project hosted in the cloud, it will eventually require a subscription (probably around 2-3 eur/month) but it will always offer a free account type (probably with a limit on the number of devices).
I have no plans on developing the current version of NORA any further but also, no plans to bring it down.