Your Early Arm Bend Is Not The Problem
Weightlifting Coaches seem to spend a lot of time arguing semantics and personal philosophy, rather than arguing the facts about weightlifting (see Catapult vs Triple Extension). Most of the time, they're arguing the same thing, but they just want the ability to say "Yes, I was right in the way I was saying it." Weightlifting Coaches are a silly bunch, and maybe one day I'll tackle the Catapult vs Triple Extension argument, but not today. It's a bit overdone and boring, so rather than that, we'll look at something that's almost as hotly debated: the Arm Bend.
As these things go, we have two camps: Arm Bend and No Arm Bend. The first camp believes that you should be able to pull the barbell into your hips more to allow the body greater power delivery with the hips and legs; while the latter camp believes that you should keep your arms long while placing the bar into your hips or upper thighs to allow greater power delivery with the hips and legs, otherwise, you'll miss the lift and the unholy spawn of satan will break through the floor beneath you and drag you to hell for bending your arms. The reality is that they are both somewhat right, and somewhat wrong.
The issue with the arms is not whether you are keeping them straight or bending them in to the hip, but are you keeping tension on the bar? Whether or not you bend early with the arms or keep them long until after the leg and hip drive at the top of the Second Pull, the only thing that matters is if you keep tension on the bar and generating momentum. Let's take a look at two lifters, both who have different arm actions:
Rob, on the left, has a much more pronounced arm bend as he gets the bar past his knee caps and into his hips. Colin, on the right, keeps his arms straight (or as straight as you can, there will always be a little bit of flexion in the elbow) as he gets the bar into his hips. Both are lifting heavy weight with different arm actions. Why is this? Why do people who miss weights off their hips during the second pull both do it with straight arms or bent arms? It's because you're not keeping tension on the bar either way.
If you find yourself getting the bar to the hips and you drive the legs during the second pull, but you are slow or have no speed under the bar, the issue is you're letting your arms and shoulders relax as you finish the pull, robbing you of momentum on the bar, or connection with the bar. A common issue with a lot of beginners is that once they get the bar past their knees, they bend the arms to get the bar into the hip immediately, rather than adjust the body around the bar. When they learn how to adjust the body the arm bend is still there, but at the top of the Second Pull, they release that tension, and their arms extend as they drive their legs, and their shoulders loosen up. Both of these actions will rob the bar of upward momentum, effectively negating all the work you just did to get the bar up.
Both camps, when they loosen in the shoulders, are effectively floating in the air momentarily, and with that loss of tension, the bar can go any number of directions - away from the body, upwards like you intended, or maybe backwards if you over pull to compensate the tension issue. Either way, the lifter will have to try and get tension back on that bar quickly if they want to change direction, but even a momentary lapse in connection with the bar can mean a missed lift. How do you fix this? Simple: don't stop pulling on the bar.
Whether you're an arm bender or straight arm lifter, you need to keep constant tension on the bar to effectively change direction once you've completed the Second Pull. The moment you finish that leg drive and your body is fully extended, you should immediately feel your arms pulling on that bar and pulling you under it, as you're picking your legs up to assist in the change in direction. You are not trying to pull that bar up higher, but rather pull yourself under; imagine that you're a gymnast on the Bars - the gymnast cannot move the bars around, as they are bolted down to the floor, so they are going to have to move around the bars. This means flexing and bending your body at the right times in junction with your momentum to execute a skill, but also at certain times pulling and pressing against that bar to make a skill happen.
The same principle applies to weightlifting, just on an apparatus that moves with you. At a certain point, you're not going to be able to pull that bar any higher, either with your arms or legs, so you have to learn to pull on the bar, with the goal of moving your body, not the bar. So whether or not you bend your arms or keep them long and straight, that's not going to make or break you; but whether or not you can keep tension on that bar so you can change direction quickly and effectively, that will be all the difference in the world.