The worst bug ever

Did you maybe skip a planet? If you are facing mobs 4 levels higher than you, you are under leveled for the planet. Level 26 mobs sounds like you are on Tatooine or Alderaan, while your level says Nar Shaddaa, did you do all the planets your class story gave you? in my years of playing, I have encountered so many under-leveled players on Nar Shaddaa that skipped the previous planet because they are given two planets in their class story, with no clear indication that they should do a certain one first.

Depending on which side you are, you should be doing:

Hutta/Korriban>Dromund Kaas>Balmorra>Nar Shaddaa>Tatooine>Alderaan for your class story up to end of Chapter 1 for Imperial side,

or,

Ord Mantell/Tython>Coruscant>Taris>Nar Shaddaa>Tatooine>Alderaan for your class story Republic side.

The story is designed for them to be done in this order, and if you skip a planet, especially as f2p or preferred, you will end up under-leveled and have a really hard time.

It is also possible you wandered into a heroic area, but most of the time the heroic areas are a much higher level  (or at least they used to be, that might have been changed).

If you are f2p or preferred, you need to do some of the planetary story arcs in addition to class story to keep your level up (and heroics wouldn't hurt either).

Either way, doesn't really sound like a bug, sounds more like a missed planet, wandering into a heroic area (if they still have some with much higher levels than the rest of the planet), or just not doing enough missions on each planet. 

If you check the galaxy map, it should give a level range for the given planet, you should try to go to each planet no more than one level lower than the minimum, and try to leave the planet no lower than one level below the maximum, that will keep you from facing mobs 4 levels higher.