We noticed that Flow wasn’t working in IE11 or Edge, but was fine in Chrome and Firefox.
It turns out that IE11 and Edge need the webcomponentsjs folder to be present.
When building our project locally, the webcomponentsjs folder was being created correctly from the maven build. However when the maven build ran in Jenkins, this folder wasn’t being generated. We eventually found the problem was due to the path having brackets in it (C:\Program Files (x86)\Jenkins)
There is an issue for this in the copy-webpack-plugin which has already been fixed - https://github.com/webpack-contrib/copy-webpack-plugin/issues/266
Hopefully Vaadin Flow will use this newer version with the fix soon.
For now we are using a custom workspace which doesn’t contain any brackets.
I hope this helps anyone else having this issue.