I can confirm that REC/RPL windows are a little bit buggy on Linux. On windows I did not experience so much troubles.
I have the same problem as Kedavidsa running Capella 1.3.0 and 1.3.1 on OpenSUSE 15.1 running the system default Java 8. Details of Java below.
openjdk version “1.8.0_222”
OpenJDK Runtime Environment (IcedTea 3.13.0) (build 1.8.0_222-b10 suse-lp151.2.3.1-x86_64)
OpenJDK 64-Bit Server VM (build 25.222-b10, mixed mode)
After starting, the first RPL instantiation works. However, any subsequent attempt at creating a RPL does not succeed because the dialog keeps saying to ‘Select a REC to create a RPL’ even after a REC is selected.
Maybe it is a problem with this specific edition of Java? If not, what would be the right place to start a bug report?