Saw this mentioned on a couple of Reddit threads too and nobody had a decent explanation. The FAA does issue TFRs without public reasoning fairly regularly but usually theres at least some vague category attached - VIP movement, military exercise, that sort of thing. A completely blank restriction with no associated NOTAM detail is genuinely unusual and worth digging into.
Anyone managed to pull the actual NOTAM reference number? If you've got that you can cross-reference with FlightAware and ADS-B Exchange to see what if anything was actually flying in that airspace during the window. Sometimes the absence of traffic is more interesting than the presence of it.
Not saying its definitely something weird but Nevada airspace anomalies have a pretty solid track record of turning into something worth following. Would love to know the exact coordinates and duration if someone has them.