Errors In Syslog: IPDL protocol error and PClientManager::Msg_ForgetFutureClientSource Processing error

I keep getting the following errors in syslog:

021-11-22 10:17:19 Nov 22 10:17:19 *desktop-id* plank.desktop[4478]: ###!!! [Parent][DispatchAsyncMessage] Error: PClientManager::Msg_ForgetFutureClientSource Processing error: message was deserialized, but the handler returned false (indicating failure)
2021-11-22 10:17:19 Nov 22 10:17:19 *desktop-id* plank.desktop[4478]: IPDL protocol error: Handler returned error code!

Googling IPDL-errors show references to Google freezing problems. However, that does not happen here. The errors seem to have no effect. What are these errors about? Thanks.