Here is the message from my DM:
It's been getting kind of ridiculous. This is the third time we've had a situation where something happens unexpectedly or someone makes a sudden move, you can't be surprised ever, and then you roll a higher initiative, so it's like "This guy didn't make his move yet, but you just had a HUNCH he was going to suddenly cast Misty Step" or "PC didn't do anything yet, but you can just sort of tell that they are going to suddenly kick this guy". This isn't Diviniation magic, and you're not a Jedi, there's no way that being more "Alert" would cause you to predict events before they happen.
Comments?
Ok, there are situations like this where Alert doesn't make sense, you react to something before it happens. And perhaps because you react, the trigger doesn't end up happening after all. So what did you react to?
My response to that is that rolling for initiative, like any other roll in the game, is meant to reflect the effects of chance on events and resolve outcomes in a neutral way. For any roll, if the DM doesn't think the outcome is uncertain, it is fine to simply not roll and just say what happens. Like if you set up an opportunity to make an attack that simply can't miss, the DM can just say it hits. The DMG totally backs this up.
Similarly, if you're in a situation where one character simply has to go first based on what is happening, just have them go first... if you like, assign them a very high initiative value. If the situation isn't that extreme but it seems like one character should have an advantage, give them advantage on the roll.
That doesn't really nerf Alert. You still can't be surprised, whether you go first or not. And the initiative benefit should normally apply; situations where initiative isn't random ought to be fairly rare. The fact that you've seen it three times already is, to me, a lot. But it's still only once per level.
Feel free, as a player, to argue your case... if you were about to be attacked by a sniper, maybe you caught a glimpse of the weapon just before it was fired. But if the sniper was in darkness, with a good Stealth check, and you don't have darkvision, then maybe you just let it go. In either case, let the DM have the final say, that is their job.