From the wiki:

The following things cannot be fixed without changes to Bedrock or the Java protocol in general...

    - Blocks (excluding jack-o-lantern) on entity heads (E.G. armor stands, players)

If the head of an Armor Stand uses an unsupported block, have GeyserHacks display it as Carved Pumpkin instead of naught. Particularly useful for Spigot plugins such as GPS.

Please leave an issue for this on the main Geyser repository. This is something we can accomplish without server-side hacks.