I am aware of solutions that use "can" or "will" to circumvent the issue, but I really want to know the answer. In the sentence below, "efficacy" is what I want to center on. It is what "that" describes. However, the word "that" immediately follows "gamification mechanics", which got me confused.
Cross-platform comparison of multiple pro-green programs will be a valuable addition to the literature because it helps researchers measure the efficacy of gamification mechanics that is/are particularly robust in some situations but not others.
If you have better ways to rewrite the sentence without contorting or undermining the message, please share.