to be sluggish; to make little progress; to show little growth; to fail to improve; to level off; to not grow as much as expected
売り上げが今月も伸び悩んだ。
Sales were sluggish again this month.
チームの成績はここ数ヶ月伸び悩んでいる。
The team's results have been sluggish for the past few months.
実力があっても環境が悪いと伸び悩む。
Even with ability, you stagnate if the environment is poor.