This bug was originally entered back in 4.8 as [Link Removed], but was closed as by design. The reason was, the mesh did not have Lightmap UVs, so using the 'Light as If Static' option would not work.
I offered this as the suggestion to the user initially to see if it fixed the issue, but he returned with an entire project full of cleanly UV mapped actors that were experiencing the issue.
I requested he reproduce this in a blank project with some very simple primitives, and he was able to reproduce the issue after testing a lot.
"It's still not a concrete and clear issue, but to me this shows some evidence that the startup settings are affecting the chances of failure. Maybe there is a simple logic error in the level loading and level saving scripts?? Just grasping for an explanation since this bug has been around for close to a year now" - StephaBon
1. Make a blank blueprint project with Starter Content
2. Clear all the editor and game startup maps in the Project Settings
3. Set the default Starter platform to Movable, check the "Light as if Static" checkbox (LAIS)
3. Build lighting, save the map and close the project.
4. Re-open the project, save, close, and repeat.
Outcome The Light as if Static option will sometimes uncheck itself.
Expected The option persists no matter how many times you close and re-open the project
Note This reproduction case takes a good amount of iterations for it to appear.
Head over to the existing AnswerHub thread and let us know what's up.