Version 5.0.1 was released on Feb 07, 2020! This is a patch release which fixes several issues reported in version 5.0.0.
For more details, please see the Release Notes which are now available from the program Help.
A problem has also been identified in version 4.2.2 which affects versions 5.0.0 and 5.0.1. The Easy Add/Multiply Editor dialog should not be used to combine a plugin model with a built-in model, or to combine two plugin models. In version 5.0.0 the operation will fail (generating an error message in the Log Explorer). Whilst in version 5.0.1 the operation has been blocked until the problem can be fixed. If it is necessary to generate a plugin model from more than two built-in models, please edit the plugin model .py file directly and specify the combination of built-in models required. Further information is available in the Fitting Data section of the User Documentation.