When using the Scale with Screen size option in the Canvas, when you press the play button the UI for some reason just spawns of the canvas, please fix in 2019.3 Beta 7. I tried it in 2019.2.8 worked just fine.
Are you sure your anchoring is right?
I am sure because I tried it in 2019.2.8 and it worked just fine no anchoring even required.
If it works with an earlier version than Unity 2019.3 beta, then you probably found a regression. In this case Unity Technologies wants us to report these issues as described in this document:
It’s important that you report these issues together with a reproduction project if you want them to get fixed. If you don’t do it, it might be a long time until someone else reports them or until Unity Technologies find them.
After you submitted the bug-report, you receive a confirmation email with a bug-report Case number. Please post the Case number (number only, not the link) in this forum thread for Unity staff to pick up.
I just dont understand how to report