Vaadin Application automatically changes theme to dark or light on startup

I am using vaadin business app starter to develop an application. Suddenly I have met an issue, whenever I run my project, sometimes the project opens in dark theme and some times in light mode. I don’t know why. Vaadin business app had already came with this code for theme; @Theme(value = Lumo.class, variant = Lumo.LIGHT). That simply means it will always open in LIGHT theme. I also removed the particular line but that also didn’t worked.

If anyone can help me out of this issue, that’ll be a great help.