Regarding questions

Sir I solved various challenges questions yesterday itself and it showed me “success” too and tick appeared in front of that.
But today I noticed, the tick has been disappeared from some of the questions. The same happens in case of lectures too
The tick disappears on its own. Which helps me to distuingsh solved and unsolved problems.

For example; the question of identifying armstrong number was of them.

Sir i request you to kindly look into it.