I have just installed the newest dev-version and get the two windows when opening JabRef. The second one is the normal JabRef, but the first one is like a command line, with JabRef logo and title containing the following message:

"ERROR StatusLogger Log4j2 could not find a logging implementation. Please add log4j-core to the classpath. Using SimpleLogger to log to the console..."

Version: JabRef-5.0.0.msi (2019-11-15)
OS: Windows 7x64