A since-deleted statement released by the Vegas race on its social media platforms read: "Due to logistical considerations for our fans and our staff, we have made the determination that we will be closing all Las Vegas Grand Prix fan areas at 1.30am. We look forward to welcoming fans back later today for exciting FP3 and qualifying sessions".
The development meant the FP2 session took place in front of empty grandstands and finished at 4am, the time the sections of track that take in public roads were supposed to be fully open to the public.
Autosport understands that fans had to leave the fan areas due to security team shifts ending, which meant the grandstands and fan zones could not operate as expected.
It is not currently clear why the original statement was deleted from the Vegas race's social media accounts.
But a later statement said: "There is no higher priority at a Formula 1 race than the safety and security of drivers, fans and staff alike.
"Following last night's incident involving a water valve cover, the Las Vegas Grand Prix, F1 and the FIA decided to take extra precautions to ensure the integrity of the track prior to the resumption of racing.
"These additional measures required multiple hours to fully complete, which led ot a significant delay in the race schedule.
"Given the lateness of the hour and logistical concerns regarding the safe movement of fans and employees out of the circuit, LVGP made the difficult decision to close the fan zones prior to the beginning of Free Practice 2.
"With a full round of practice successfully completed, LVGP looks forward to providing a safe and entertaining race weekend for all."
The heavily delayed timetable for the first day of F1 action in Las Vegas for 41 years was caused by the cancellation of the earlier FP1 session following Ferrari's Carlos Sainz and Alpine driver Esteban Ocon striking a loose water valve cover while traversing the lengthy Las Vegas Strip section of the 3.9-mile track.
Race officials and track engineers have made rapid inspections and repairs to 30 such water valves along the Strip – by filling them in with a mix of asphalt and resin that is hoped will keep them in place sufficiently when the cars are running over them at top speed on such a long straight.
The big forces produced by ground-effect cars on the track as cars move across it have been cited as a reason why the water valve cover in question failed, something that happened specifically around its concrete join with the rest of the road.
FP2 had finally been rescheduled for 2am following the repair efforts, before this was pushed back first by 15 minutes and then a full half hour to commence at 2.30am local time.
