[ENH]There is an issue with the IF activity in Elsa 3.1.3 designer

Hello, teacher

In Elsa 3.1.3 designer, if an IF activity displays two buttons in the activity display, Then and Else do not work. If you click the "Then" or "Else" button, it is not possible to logically drag and drop a new activity into the sub flowchart? Is it not possible to visualize IF activities in Elsa 3.1.3 designer?

Start by reproducing the issue in the Elsa 3.1.3 designer using the attached IF activity example. Check the Then and Else controls and their drag-and-drop behavior; it is done when activities can be added to both sub-flowcharts as expected.

Written by the indexing model from the issue text.