Two years ago, Twitter Inc. Chief Executive Jack Dorsey issued 13 tweets emphasizing the need to make conversations on the platform less toxic. Mr. Dorsey said Twitter needed to work with outside researchers and hold itself publicly accountable for its progress.

Now experts working with the company say those efforts have stalled, and some worry that Twitter’s commitment last week to boost growth—made in response to pressure from an activist investor—could further complicate those attempts.

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