For the most part, Avengers: Infinity War is an incredible achievement, weaving together threads from eighteen films into a cohesive narrative that began the climax of a decade-long meta-narrative. However, there was a glaring plot hole in Infinity War, and it all has to do with the Infinity Gauntlet. Namely, if Thanos had Eitri make him the gauntlet to harness the power of the Infinity Stones, then how and why did Odin have a fake gauntlet in his vault years prior in the first Thor movie. Well a fan has come up with a theory that may explain all that.
Prior to Avengers: Infinity War, the Infinity Gauntlet appeared thrice. It first appeared as an Easter egg in Odin's vault in Thor. In the mid-credits scene for Avengers: Age of Ultron the gauntlet showed up again, this time in Thanos' possession in his "I'll do it myself" moment. That created a conflict because how does Thanos have the gauntlet if it is in Odin's vault. That problem was resolved in Thor: Ragnarok by Hela explaining it away as a fake. But that third appearance created the issue for Avengers: Infinity War when we learn Thanos had Eitri make him the real gauntlet. The explanation for all of this, according to Reddit user cgcs20, is that the concept of the weapon existed prior to Thanos' quest. Thanos' wasn't commissioning an original weapon, but asking for one based on an already existing blueprint. And who first had the Infinity Gauntlet designed? Why none other than Odin himself.
Thor: Ragnarok illuminated Thor and the audience to the fact that Odin wasn't always the sweet old All-Father we saw in the first two Thor films, as he was once a conqueror with a love for war and little regard for life. According to the theory, Odin too once sought the stones and he had the dwarves of Nidavellir create a replica or demo unit of the Gauntlet for him. When he turned over a new leaf and covered up his warlord past, he put the fake Gauntlet away in his vault, perhaps as a reminder of the power he once sought and the destruction that desire caused. This would have disappointed Hela, thus explaining how she knew that it was a fake.
Another Reddit user actually expounded upon this theory, offering up the possibility that Odin gave up his stone quest when he was unwilling to sacrifice Hela for the Soul Stone, thereby revealing himself to be soft and unworthy to rule in her eyes.
Overall this is a really compelling theory that fits in well with what we learned about Odin in Thor: Ragnarok and helps explain why Odin had a fake in his vault. What this theory doesn't really clear up is the Avengers: Age of Ultron mid-credits scene where Thanos decides to take matters, and the real Gauntlet, into his own hands. However, that too has a workaround. For one, we don't know how long Nidavellir has been dark or when Eitri created the Infinity Gauntlet for Thanos. Also, you could say that the mid-credits scene for Age of Ultron does not take place in the same time period as the rest of the film.
What's cool about all of this is that way back in 2011, the gauntlet in Odin's vault in Thor was probably just put in as a fun Easter egg, with a 'we'll deal with it later' mentality with regard to how Thanos would eventually get it. The same goes for the Age of Ultron credits scene. However, story plans change over time and discrepancies arise, but none of them are so bad that some clever thinking can't come up with a good explanation for them.