Ok, this may seems like a stupid question but is there any reason for or against using light armor and a heavy shield? Like does having a heavy shield somehow create a problem with light armor?

It will not create any problems, it just wont benefit from any light armor perks.
Spellbreaker?

Shouldn't cause too many problems. The main issues with mixing armor types are:

1) You wouldn't benefit from the Custom Fit or Matching Set perks, but since shields aren't factored in there should be no issue in what you're proposing.
2) You'll get skill-ups in both Light and Heavy Armor as you fight, but that's not really an issue unless you consider it a problem that blocking with a shield will siphon skill leveling away from Light Armor because you weren't struck on a light-ly armored body part.
3) Nazeem in Whiterun or Taarie from Radiant Raiment might make nasty comments because your clothes don't match.

Your character doesn't have to have a matching shield. However, it does mess with your skill increases, mixing your stat gains in light + heavy armor. Most of the guards shields are light armor, and they have some have a cool coat-in-arm that is etched into the wood. There is also a light shield that causes bleeding damage, though I cannot remember exactly how it is obtained. Or you can just enchant the crap out of any shield. I prefer the lighter defensive gear, myself.

Targe of the Blooded
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