The track action was halted as a precautionary measure with 20 minutes to run after a marshal reported the problem just before Turn 17 of the floodlit street circuit.
Red flags were then waved again with just over two minutes remaining to end the session shortly after the drivers had returned to the track following a 15-minute delay.
The governing body, FIA, said on-site personnel had reported that the same manhole cover was still shifting as cars passed over it, and the situation was checked as a precaution.
Loose drain covers were a problem in practice for the inaugural Las Vegas Grand Prix in 2023, with one wrecking Carlos Sainz's Ferrari when he drove over it.
Norris, who has a 24-point lead over teammate Oscar Piastri going into the race with three rounds remaining, produced a best time of one minute, 33.602 seconds on the soft tyres after Ferrari's Charles Leclerc set the pace in practice one with 1:34.802.
"We didn't manage to get too much from FP2, given the disruption, but we did get a slightly better feeling than in FP1," Norris said, referring to the two practices.
"We made some good progress, and we've got a reasonable feeling altogether. Some positives to build on and some areas to try and improve going into tomorrow."
Norris had brushed the wall without damage in that opening session and was sixth, while Piastri was eighth.
The Australian was 14th in the second practice after having to abort a quick lap before the first red flag, and not getting in a lap on the softs, with McLaren looking more competitive on the evolving track.
Mercedes' Kimi Antonelli was second, 0.029 slower than Norris, and Leclerc third, the Monegasque stopping with four minutes remaining.
"Something broke. Gearbox. Can I shift or not?" he asked over the radio, his race engineer telling him not to.
The Williams of Alex Albon was second in the opening practice session, with Red Bull's Yuki Tsunoda third and four-times world champion teammate Max Verstappen fourth.
Verstappen was ninth in the later session with his time set on medium tyres, one of several running out of time to try the softs.
McLaren have cautioned repeatedly in the run-up to Las Vegas that they are likely to face a tougher time at a track that has not favoured them in the past.
"I think this could be a tricky weekend," chief executive Zak Brown told Sky Sports television halfway through the first session.
The opening session was on a dirty and unrepresentative track, on streets used by regular traffic, but Leclerc was on the pace from the start, with teammate Lewis Hamilton only 11th.
