Custom Session Property in Ignition got deleted

[pascal.fragnoud]

See this thread concerning disappearing session customs:

Perspective Session Props:

Hi there! This is Ganapathi. I’m facing some serious problem in session props attribute. An attribute named “host” is not listing under the session props (occasionally its disappearing). However, when I close and re open the ignition app it is listing. If you guys have any workaround for this. Software version : 8.1.20

On the subject of the theme, though, that's the first time I've ever read about this issue.
What ignition version are you on, and how are the themes set up ?