Q&A in Webinar is there a limit?

Hello,

There is no limit I am aware of for this feature. If you have the participant capacity it should be available as far as I know. I know breakout rooms have a limit of 1000.  I suggest you submit a ticket with Zoom support (https://support.zoom.us/hc/en-us/requests/new)  to be certain.

Are you sure it wasn't user lack of knowledge on how to make use of the feature since it worked for some?

Zoom require users to be on a minimum version for certain feature to work. I think 5.10.3 is currently the global minimum. It may be different for mobile devices. 

Prerequisites for using Q&A in Webinars

• Zoom desktop client for Windows, macOS, or Linux 
• Zoom mobile app for Android or iOS
• Host is a licensed user with the Webinar add-on
• Q&A in webinars enabled

Regards

What capacity of participants was your license?

5000 participants 

This is quite an unusual situation, however, it is likely that the participants who could not see the Q&A section did not have their Zoom application updated or if they entered the webinar through the web portal, they have limitations with some functions.

It is recommended as long as they download the application and enter the sessions from that medium.