Having worked for many years on the Frequentis 3020 in our system;it would be interesting to know if new software had just been installed.
Te procedures we developed would have us have had us take down one of the parallel / redundant switches, (leaving the operation with no redundancy within the switch, but we had completely independent backup system to provide all comms just in case) and load and TEST the software while that switch was offline. If all went according to plan the switch with the new software was brought on line and the switch with the old software taken offline (making sure that the two versions of software didn't try to talk to each other)
If the new software proved itself under real world use for a while then the other switch was updated, and tested, then switched back on line. The fact that the 3020 allowed either switch to fully support the operation on its own made helped make upgrades a lot easier. In dozens of software upgrades I don't think we ever left the operation stranded, a couple of times we had to switch back to the old software due to problems that never seem to show up in the lab but are happy to raise their ugly little heads when used in anger.
Would be interesting to hear what process NATS used for the upgrade.