[Gareth]

Does the LOS restriction apply to sustained spells once cast?

The section on recognising magic (P. 129 seems to imply so),

i.e.: If I cast a spell and then move to a point from which I can no longer see the target area does the spell end partially or fully?

Do area spells still exclude targets not seen but within the area?

[Shinobi Killfist]

Generally no. In 6e for reasons unknown the levitate spell in particular requires maintaining line of site while sustaining the spell

[Stainless Steel Devil Rat]

Does the LOS restriction apply to sustained spells once cast?

I don't believe this is the case. Uncertain as to whether you can sustain a spell cast on a target that was valid at the time but you've since switched planes, however.

Do area spells still exclude targets not seen but within the area?

This is unfortunately unsaid.  Clearly, in prior editions this was the case.  This time around, it never says people unseen go unaffected.

[Shinobi Killfist]

The description on noticing magic I had taken for spells that require some level of control. Like maintaining a improve attribute spell nothing is needed just sustain it. Now if I make an illusion of a mech landing in downtown I can’t make it react and do actions that make sense without keeping an eye on things. But maybe it’s changed in 6e and they just weren’t explicit here. If so what a royal pain in the ass to pay attention to.

 I don’t want to keep track of whether or not a player constantly has line of site. I’m assuming blinking doesn’t count but does a flash bang or a flash pack, just seems a hassle for the GM.

But since they explicitly call it out for levitate(again no idea why, the spell wasn’t broken outside maybe 200kg a hit on min maxed pools might have been slightly too much, though 50kg seems a large over correction) that makes it sound like an exception.

[Typhus]

For Levitation it makes some degree of sense in general, but it does establish a change to the magical world by doing so.

As a concept, you would need and want to guide your target to the destination, not smack them into beam, light poles, zeppelins, whatever.  If you lost LOS, but maintained concentration, they would presumably either just hang in mid air or else continue on the same trajectory you had them on previously.  Therefore, you "need LOS" on the spell, but that may only be in the context of moving the target. 

SR doesn't have a "Line Of Effect" clause on spellcasting, meaning once cast, nothing can break the effect other than in the case of Limited range spells.  If I cast Armor on the street sam, it stays until I drop it.  They can be around the corner or around the world.  Same with Mask.  I have to touch them to cast it, but I don't have to stay in contact.  It's just not stated to the contrary.

5E Area spells: "All targets in the area of effect that you can see, friend and foe alike, are valid targets for the spell. If a potential target is outside your vision (behind a screen, for example), they’re not affected." So by this rule, even a fireball that detonates behind a point of cover will not hit targets you know to be hidden behind that cover, because you could not see them at the time of casting.  No matter the radius and the fact that the ball of fire will roll over the top of them.  This rule also contradicts the "bouncing spell" AoE mechanic elsewhere where AoE spells have scatter for the first time.  But I digress.

5E Levitate: "The subject of the spell can be moved anywhere in your line of sight at a movement rate equal to the spell’s Force in meters per Combat Turn."  No rules on drops or what happens if you lose LOS.

So, thus you would need LOS to cast it, and LOS to move them.  However, 5E does not appear to have a ruling on things otherwise.  If a character who was in range and in LOS of a spell at casting, but then moves out of LOS (but stays within range), there's no rule on how to handle that. Conversely however, if a character leaves the range of a Limited spell, they are no longer affected by it.  No rule here = it's up to the GM.  It would not be unreasonable to say going out of LOS breaks the spell effect.  It's consistent with other mechanics.

However, with 6E, the description establishes only a single-case change to the game universe that was never explicitly true in any prior edition:
"The target has to stay in sight if you want them to stay in the air; the minute they’re out of sight, they’ll be earthward bound."

This implies but in no way can be confirmed that the same should be true for other such LOS spells being sustained.  It could be either Levitate specific for some crazy reason, or true of all LOS spells (and just not mentioned thanks to committee based rules design and all the other problems with the rules-writing in the game).  They have changed the metaphysics of the game world in 6E, so nothing can be assumed any more.  There are no more Limited Range spells, only Limited Duration spells, which is completely new and unprecedented (for a good reason--"fire and forget" spells are one of the very poor rules decisions in 6E).  So you really are left guessing at the intent here.  There's no wrong answer. 

Instead, the answer is: Like most of 6E, it's up to your GM to write the rule until and unless the designers decide to do so.

Good luck!

[Shinobi Killfist]

Yeah I guess up to the GM. My take on the levitate is that it is a levitate only exception as if it was the general rule they wouldn’t need to mention it. In previous editions I get not being able to control it without line of site but it never ended the spell. If that is a general change I don’t think it was a good one. Yeah it limits magic which it is too powerful but it does it in a poor way that makes it just more fiddly and more of a pain in the ass instead of actually limiting it.