Here is the User Guide info about drag-and-drop: Drag-and-Drop Questions in Storyline 360 - E-Learning Heroes (articulate.com). And if you look through the on-demand training (Watch Storyline 360 Webinars - Articulate 360 Training), you'll find more info.
There's no limit to the number of drag-and-drop activities allowed within a project.
When you're having a problem with Storyline, it's best to upload a copy of the .story file. That'll make it much easier for someone to troubleshoot. Here are the best practices for sharing a file:
- Make a copy of the file with only the slide(s) involved in the issue.
- Be sure everything (e.g., objects, layers, variables) has a meaningful name.
- Replace any proprietary content with alternate text (e.g., "ipsum lorem" text, or just "yada yada yada").
- As much as possible, provide details about what you want to happen, what you've tried, what is happening that shouldn't happen, and/or what is not happening that should happen.