Retrogression or deterioration — the opposite of progress; used as a noun or in the verb form 'to regress/retrogress'.
技術が退歩したわけではなく、運用方法に問題がある。
It's not that the technology has regressed; there are problems with how it's being used.
練習を怠ると技能が退歩することがある。
If you neglect practice, your skills may deteriorate.
近年、自由が退歩したと感じる市民もいる。
Some citizens feel that freedoms have regressed in recent years.