Learn Why Users Are Switching Back to Salesforce Classic
Where: This feature applies to Lightning Experience in Group, Professional, Enterprise, Performance, Unlimited, and Developer editions. Chatter must be enabled.
Where: The feedback form was made available in late August 2018.
Why: The feedback form appears when users switch to Salesforce Classic. Choose whether to keep the default feedback question or write your own. Select how often the form appears and in which public Chatter group to store the feedback.
Users write the reason, which is posted in your chosen public Chatter group. Users are notified in the form that their feedback is shared in a public group where everyone can contribute to the conversation and see other commonly asked questions. Users aren’t required to add feedback before switching back to Salesforce Classic.

How: From Setup in Lightning Experience, enter Onboarding in the Quick Find box, and then select Onboarding & Assistance. Turn on the feature under Switch to Salesforce Classic User Feedback Form.