https://bugzilla.redhat.com/show_bug.cgi?id=1840743
--- Comment #5 from Douglas doug.hs@protonmail.ch --- I have managed to get everything working now by deleting all workspaces, installing eclipse-mpc and creating a new clean workspace on first startup of Eclipse.
So, to reproduce this, start with an existing workspace and then install eclipse-mpc. Eclipse will fail to start. Now remove eclipse-mpc. Eclipse starts, but workspace is broken and the Eclipse installation complains about missing eclipse-mpc files.