Quite often but not always the the following happens when a user wants to transfer a file:
As soon as the sender starts the filetransfer, the Spark of the receipient gets a popup/toaster of the last msg HE sent out. When the sender opens up Spark he sees a fie transfer request and when he OKs it, everything works OK. Well most of the time it is OK; I reported some strange behaviour but did not catch that much insterest in the problem.
Our Setup OF 3.3.3 on Linux with builtin-DB with Windows Spark 2.5.5 and 2.5.6 skinned version. The only thing special in our setup is the dual homed server with one public and one privat IP-Address but NO router on this machine.