This can happen if a lead respondes or replies in a text that doesn't match the automation phrase exactly.
Once you take over the conversation from the hybrid automation, and an appointment time is determined, follow the steps to schedule the lead manually from the conversation
In the "Conversation" with the lead, on the bottom right of the screen click "Schedule"
**Select the calendar you want to add them to if you have more than one calendar
Select the date and time slot
Scroll down and click "save"