Ignition Perspective 8.1.33
Ran into this issue this morning and once about 6 weeks ago. Didn't ask anything about it then as it seemed like some one-off thing, but it happened again.
This morning, I came back into the office, I still had my designer instance open for my project, and it looked like it had some unsaved changes still pending to be saved (oops). I went ahead and saved it, and all seemed fine. I then opened a perspective session and tried to navigate around. I use a session property to handle some important navigation and utility functionality, so I noticed right away that I was having issues. I went back to the designer to check the session properties, as the last time I had this issue there were very similar symptoms. To my surprise, the session properties were still there it seemed. I then checked the logs, where I found some warnings that would line up with what I was expecting before.
It was strange to me that the perspective session was having trouble seeing the properties, but my designer session was not. After that, I restarted my designer session and lo-and-behold, the custom session properties had vanished.
Glancing at my logs, it doesn't look like the issue happened until after I saved the project, which makes me think there is some bug with saving in long-lived designer sessions (this session was probably open 24 hours and while my machine was asleep).
This is far from the first time I worked on designer sessions that had been open longer than this, but it may be the first time I saved changes that were pending from yesterday. Hard to know. Does anyone have any insight as to what might have caused this issue?
Luckily I had a backup that I was able to reimport the session properties with, but otherwise, I would have had to recreate everything from scratch.