Unicode escape sequences, as described here in the OptiFine documentation, do not function at all when used with Continuity; this is most notably problematic for resource packs that make extensive use of Minecraft formatting codes in block entity names to customize their appearance.

When using a standalone setup of OptiFine HD U J3 on Minecraft 1.21.4, block textures change as expected when Unicode escape sequences are used in their .properties files in a resource pack:

When using a Fabric setup consisting of only Continuity 3.0.0, Fabric API 0.116.1, Mod Menu 13.0.2, and Text Placeholder API 2.5.2 on Minecraft 1.21.4, textures don't change at all for the same blocks, despite having the same resource pack enabled (this also applies to other block entities, not just beacons):

The resource pack I created to demonstrate this can be found here: UnicodeTestPack.zip

My latest.log from the Fabric setup can be found here, if needed: https://mclo.gs/ZAY0pIN

Are you sure this is not a duplicate of #449?

By my understanding, yes, this is a completely different issue. Block names that don't use Unicode escape sequences behave as expected when placed, whereas ones that do use them never work at any point.