'this stagnant problem' is not a sentence; a sentence requires a subject and a verb. This phrase could be the subject of a sentence if you add a verb:
This stagnant problem has bothered us long enough.
The stagnant water was unsafe to drink because it was not moving.
Active, energetic, and dynamic are a few antonyms of stagnant.
Mobile
"Complex", in this sentence, is used as an adjective. It describes the problem, a noun.
it means in what way did you go about investigating this problem.
Do not refill your canteen from stagnant water. I left the company because my career became stagnant.
The stagnant water smelled nasty.
methane is produced in the stagnant water in rice fields...
The stagnant water was unsafe to drink because it was not moving.
The water in the stagnant pond quickly took on an unpleasant smell.
The stagnant water tasted disgusting which made me immediately spit it out in the sink, impolitely.
The elephants gathered around a stagnant watering hole since they were too tired to look for a freshwater source. The stagnant water smelled awful.
Unlike rushing water in a river, water in a pond is stationary and stagnant. 1 stagnant water or air is not moving and therefore smells unpleasant: Few fish survive in the stagnant waters of the lake. 2 not developing, growing or changing: The new investments are aimed at reviving the stagnant economy. The housing market has been largely stagnant over the past few months.
The word toppled is used as a verb. Endemic corruption, a stagnant economy, and massive public protests toppled the regime.
Active, energetic, and dynamic are a few antonyms of stagnant.
Stagnant culture refers to a situation where no significant changes or improvements occur in the beliefs, practices, or traditions of a group or society over an extended period of time. This lack of evolution can result in resistance to new ideas, growth, and progress.
That's your problem.