As the attached image shows, there is no problem in 4.25.4, and the process is noticeably slower in 4.26.1.
Also, there is no problem in Standalone.
The problem occurs only in PIE.
1. Implement a simple tick process in the level Blueprint as shown in the attached image.
2. PIE to check the FPS.
1. Open the Untitled.umap of the attached project.
2. Check the FPS in PIE.
3. If you compare the above FPS between 4.25.4 and 4.26.1, you will see a marked difference.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-108737 in the post.