"不断发生后效" can be translated as "continually producing after-effects" or "constantly having follow-up impacts".
Here are two example sentences to illustrate the usage:
1、 The policy adjustments made last year are continually producing after-effects on the current market situation.
(去年进行的政策调整正不断对当前的市场形势产生后效。)
2、 The environmental damage caused by that industrial accident is constantly having follow-up impacts on the local ecosystem.
(那次工业事故造成的环境破坏正不断对当地的生态系统产生后续影响。)