Custom Session Property in Ignition got deleted

I am working on the perspective and i face a issue like my "Custom Session" Properties get deleted automatically and the theme also get changed automatically but when ever i manually enter the Custom
Session back in the designer and change the theme it is working fine.
can anyone help to find out at what case my Custom Session may get delete will be great if someone can come up with the answer for it so we can avoid the practice so it may not happen again

See this thread concerning disappearing session customs:

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 ?