If you read the article about VisionX 6 update you saw that E-Plug is also updated from 1.2.60 to 3.0.0.

We released E-Plug 3.0.0 already and 1.2.60 is not available via Eclipse Marketplace anymore. However, if you made a mistake and want to stay with 1.2.60 it's still possible. In this case, simply add a custom update site in your Eclipse settings and use following URL: https://eclipse.sibvisions.com/eplug.1.2.60

This location contains latest E-Plug 1.2.60.

The default location for latest E-Plug is: https://eclipse.sibvisions.com/eplug