With the release of v26.00, the warnings you receive when you fail to compile a material will now be considered errors. This means the author of the material will now need to correct the issue(s) before publishing.
Previously, when publishing an island, these materials would silently fail. (On mobile, the materials would show up as a checkerboard pattern. Islands that are already published will continue showing this pattern on mobile, until the materials are fixed.) Going forward, these warnings will not be silent and the island will fail to publish until the materials are corrected.