Overview
You are using Adaplets on your Forms. Input required for the Adaplet is manipulated in custom code invoked on form load event.
The same code works fine on Aurea Process (aka CX Process / SBM) 2015 SP1, but after migration to Aurea Process 2020 R1 you are getting "Cannot parse date format" alert.
Solution
Root Cause
This is caused because of the way how the load of Adaplets and custom code happens in Aurea Process 2020 R1.
When Building or Deploying an application that has a Start step or other WorkStep that is of "Form" presentation type, BPM Studio creates a corresponding .jsp file for each WorkStep, and these .jsp files are stored as part of the project under the jsp folder, and also deployed to the server as part of the application.
In version 2020 R1 in the beforeInitControls() method the initControls() methods of each Adaplet on the given Form is invoked.
This results in Adaplets being loaded in the beforeInitControls() method before the Form is loaded. Meaning, if custom code is needed to manipulate input data required by your Adaplet, and this code is triggered only by the Form load event, your Adaplet will fail because the data it needs is not available yet (NULL data) due to Adaplet being loaded sooner than the data manipulation method. This will result, for eg. for date type of data slots in the mentioned "Cannot parse date format".
This was the event trigger order in all the product versions, except two versions: 2013 (we released a patch for this version) and 2015 SP1. We had customers complaining about this, so our development team ensured that the Adaplet/form loading is backward compatible (make it similar to 7.6 version). It was fixed (restored) with Aurea Process (Savvion) version 2015 SP2 (10.0.2). This is the explanation why this is not causing issues on version 2015 SP1.
The current way of Adaplet loading is NOT considered a product bug and we don't plan to change it in the upcoming releases.
Workaround
As a workaround, you can convert your Form to a custom JSP in 2015 SP1 version and then import it in 2020 R1 BPM Studio. This way the JSP will not be re-generated and you would still be able to use the application/jsp with empty beforeInitControls() method as in version 2015 SP1.
An alternative workaround is to restructure your code and/or comment out the Adaplet's initControl() method in the beforeInitControls().