A new version of the TreeView and GridView widget is available in the App Store. In that version we fixed issues that were breaking the widget in newer versions of the Modeler.
Give the same widget a go and see if it works in 5.19. For us the GridView widget was working fine in 5.19, but caused an endless refresh loop in 5.20.
As TreeView and GridView share a lot of code it would make sense that you have run into the same issue.
Anyone know if there is an error log somewhere for the treeview widget so i can try to debug it. Reverting back to 5.19 is quite a lot of work. and in the end it should work woth 5.20 anyway.
They released a new version, it is working now