File attachment issue with custom apps

Hi there, my org is currently on public preview and the latest version is 25017.203.3370.1174. We are running few chatbot apps withing the org and since the updates, we see that the file attachment option in our chatbot app is either disabled for everyone or inconstant for few users. Checked the manifest and mad suer the file operations attribute is set to "true". No idea what's causing this issue!