Guild Wars 2

I recently started to try and get the achievements for LS2. I find myself stuck at very last one of ‘Gates of Maguuma’ the avoiding bombs one.

If I give up for a while and move to another chapter, will I have to redo the whole ‘Gates of Maguuma’ again to get back to the last bit?

None of the achievements require redoing the whole chapter. At most you have to redo that single instance. After completing an episode you can reactivate it and just go to the start of any instance for that episode to do the achievements.

But don’t reactivate it if you are working on another chapter that you don’t want to abandon, as you can have only one active LS chapter at a time.