Plugins with webapp directory cannot "generate plugin webapp bundle"

When I try to upload a plugin or install it from the marketplace I get an error eg: “installExtractedPlugin: Unable to generate plugin webapp bundle., unable to copy webapp bundle directory: com.mattermost.custom-attributes: stat plugins/com.mattermost.custom-attributes/webapp/dist: no such file or directory”

Steps to reproduce
I have an unusual setup - I am running Mattermost 9.0 Docker running on AWS ECS Fargate with EFS (although it was showing the same behavior for Mattermost 8.x as well)

Whenever I try to install a plugin that has a webapp directory it throws the error, but the GIF plugin does work.

So I took the custom-attributes plugin, deleted the webapp directory and changed the plugin config. Then it uploaded successfully (obviously I didn’t try to activate it since it was missing the webapp).

Expected behavior
The plugin would install and work correctly.

Observed behavior
A web search for this error showed that it was likely due to a filesystem permissions issue.

I’ve logged into the EFS file system and all permissions are correct, and all of the various Mattermost directories are working correctly. Plugins with only a server component are also working correctly; so I don’t see how it could be a file system issue.