Event Begin Play of Level Blueprint fires twice

hi. finally I figured out the reason. it related to using undo in project. it happened to me when Undo my blueprint and every time I undo my level blueprint eventbeginplay fired one time more than before.at first two time then three and four and…
I made a new level and I did not use Undo in my new level any more then the problem solved. and eventbeginplay fired only one time.