Why is this unlocked by the Concrete technology, instead of Gate?

That's unintended and will be fixed in the next update, thanks for the bugreport :D

I also found "LDS Heat Pipe" requiring Uranium Processing instead of Nuclear Power

I'll keep adding more as I come across them in my playthrough
Explosives+Flamethrower Turret = Military Science doesn't require Explosive tech

Those and any future ones you list here will be fixed in the next update. Thanks for notifying me of them :D (even if it's kinda embarrassing you found multiple lol....)

let me go over the rest

advanced circuit red splitters do not require red belts
blue chip roboports need both robot types unlocked, instead of only one, but that might not be fixable. same with yellow science from roboports
plastic repair packs do not require repair packs
electric engine assembler 3s are a tech node, but should be locked with normal asm3s, since electric engines are already a requirement for those in vanilla for some reason, like how blue chip beacons currently work
iron sticks from steel can be crafted before iron sticks are unlocked, but that has a similar problem with the roboports in that they can be unlocked by multiple technologies
advanced circuits from sulfuric acid does not require sulfur/ic acid
green science from asm2 and fast inserter does not require fast inserter
purple science from blue belt, bulk inserter, concrete, requires fast inserters instead of bulk inserters, and no concrete
purple science from blue chip, red belt, concrete, does not require blue chips
yellow science from lds/robot frame/blue chip and refined concrete all do not require concrete

there're also some recipes that might make sense earlier than vanilla progression has them, like electric engines from advanced circuits not requiring advanced oil processing