Chunks containing a grave marker display entity from the Universal Graves mod are not sent over to the bedrock client via Geyser. The Universal Graves is configured with the "enable_geyser_workaround" set to true.

When the chunk is to be sent the server console logs
"[tcpClientSession-5-1/WARN]: Downstream packet error! Unknown BlockEntityType: 43"
When the bedrock player approaches render distance of the marker from afar this is the only message on the server.

I am not sure what the workaround tries to do, but it seems it is no longer sufficien for Geyser.

I am testing graves-3.2.0+1.20.3.jar and geyser-fabric-2.2.0-SNAPSHOT+build.411.jar.

Technically it's bug in geyser, but you can workaround it by updating polymer library

I recompiled with 0.7.5+1.20.4 and the issue was gone.

Has the Geyser team been told of the bug?

Might be good idea to report it, as it's inconsistent with how vanilla handles them

Will you file a report on Geyser?
If not, what was the change you had to do to Polymer? Was it some block or entity that you had to supress for Geyser clients?