We have been serving 5 licenses from Macs for years allready, and lately exclusively from Mac Minis. Mostly without a trouble. First one was a Mac Mini 2009, eventually running El Capitan. It was also a file server, but was still very reliable. Uptime might have been over a year with El Capitan, and several months with Mojave. Mostly it's some OS security update which needs a restart.
Now we have upgraded to a Mac Mini 2012 with Mojave. Mostly trouble free if it's let alone, just serving the licenses, and some older files in there too as back-ups.
No special software installed, and no remote usage allowed. That's because it happened once that it ran out of memory and stalled. I tracked that to remote usage process, it had swallowed all the installed memory (almost 16GB). A memory leak I think, which accumulated the RAM problem in few months time.
Another stall happened when someone accidentally left a mouse on the keyboard, and that way the keys there then being pressed continuously. Eventually it crashed the machine.
None of that helps you obviously, I'll get to the point:
1) You could try upgrading from Sierra to High Sierra. If I remember it right, if Sierra is supported, your Mac is upgradable to High Sierra too. In my opinion plain Sierra was not so great of an OS. If this works, it was the OS + codemeter combo.
2) You might want to check your codemeter software and maybe download the newest driver from Wibu systems. You can go back to original if it doesn't help. If this works, it was the OS + codemeter combo.
3) It seems your Mac did not crash, and you were able to use it still, just the licenses where lost? Allthough improbable, that does not necessarily shut away a possibility of some hardware problem. Maybe try another Mac, just clone the server OS HDD/SSD with CCC to an external drive, and start from the external drive with another Mac. Use as a server for a while. If it works, it was something hardware related.
It's a pain to troubleshoot, and you would of course want to avoid any longer than necessary downtime, as we all would. That's why I put a list in my opinion most appropriately ordered to try track it down.
Good Luck.
AC25, Rhino6/7+Grasshopper, TwinMotion • Mac Pro 6,1 E5-1650v2-3,5GHz/128GB/eGPU:6800XT/11.6.5 • HP Z4/Xeon W-2195/256GB/RX6800XT/W10ProWS