Edit by @yaustar

In project: https://playcanvas.com/project/977066

The text is rendered and masked in Editor:

But at runtime it isn't rendered

It looks like it is related to the size/bounds of the text element which is smaller than the area that the text is rendered as seen in this video. When the text element bounds are in the area of the mask element, the text is rendered and masked at runtime.

Please watch attached video

Here's the project.

This is not a bug that happens just on play mode, I tried actually publishing and hosting the build, it has the same issue.