I work on the west coast, but what I was told by a friend who works down there was that ZMA had a nearly 10k operation day, and ERAM ran out of discrete codes to assign, and thats what caused the nationwide groundstop. The computers basically couldn't accept any more A/C within ZMA airspace....Ive never seen or heard of that before.
Like 9-10 years ago, someone at ZLA put a U2 at FL600 orbiting the entire west coast as just OTP in the altitude window, and it completely crashed ZLA's ERAM because it was trying to send the flight plan of the U2 to every adjacent facility over and over, and it crashed the system.
The main issues at the Florida Centers, especially ZJX, is just controller staffing. As pilots, you guys think of it as just ZJX as a whole, but in reality, its divided into 5-6 "Areas", that for all intents and purposes are their own facilties. Controllers only work the few sectors in their own "Area", and are not qualified to work in any other area. The FAA has let it get to a point where certain areas within Enroute facilities are beyond critically staffed, and rely on ungodly amounts of OT to run. 1-2 controllers calling in sick can completely tube an Area like that, and limit their ability to open sectors that need to be open, especially w high volume and Tstorms.
Lets say Area 1 is negotiated to have 11 people there on a day shift, to run 6 sectors that would ideally all be open. The FAA has bungled the staffing so badly over the last 30 years, that they are only able to publish the schedule with 6 people on it, and 3 of those 6 people are on OT on what is supposed to be their day off. 2 of those 3 OT people are exhausted, have life going on outside of work, and call in sick for their OT. Area 1 now has 4 people, when they are supposed to have 11. They still ideally need 6 sectors open to run their traffic. You can do the math to see that thats not going to work, and thats where some of these crazy delays over the last year through Florida have come from. Its completely untenable and IMO only going to get worse. There are Enroute areas within the FAA where staffing is so bad, it is getting hard to train new controllers because they cant afford to lose a body to be an instructor. Its wild.