This bug occurs when a model is edited in another regional and locale format. The scenario and workarounds described below are based on a German example.
Geoprocessing models that have been created, run and saved with ArcGIS for Desktop and ModelBuilder 10.4 using region and language settings for German (Germany), are not correctly displayed in ModelBuilder 10.4. Often this behavior takes place after restarting the machine and reopening the model in ModelBuilder 10.4.
For models created with ArcGIS for Desktop 10.3.1 or older versions using German language setrtings, the display is also incorrect if the models are displayed in ModelBuilder 10.4 under German language settings. For both cases, the display is as follows.
The models successfully run ModelBuilder or as a tool. It is also possible to edit and save the models in ModelBuilder.
In some cases, changing the language settings from German (Germany) to English (United States) does solve the display issue. In these cases, go to Control panel > Region and Language > Format. choose English (United States), and Restart ArcGIS for Desktop.
Optional: the regional settings can be set to any format by changing the point/comma delimiter, such as German (Switzerland).
If it is not desired to change these settings or if it doesn’t help, there is no other way to solve the display issue at this time. However it is still possible to use and edit these models.
Editing the models in ModelBuilder still works with some restrictions: