Both the Xbox and PC version of the Bedrock codebase are affected by an inability to see banner designs if the client joins Crossplay immediately (the host is unaffected).
This bug results in the topmost design coloring the banner completely if not viewed in one's inventory, but will show the base color while in the hotbar. Attempting to view the banner while in an inventory with the banner results in a crash (both platforms).
This is temporarily fixable by entering any singleplayer world before joining crossplay.
(Didn't check dedicated server multiplayer).