Invisible layer bug problem

[Beverly5E9A]

I had a couple of recent times in which while doing college assignments the current layers, for some unclear reason, became invisible. I tried to try to solve it or make it visible again. But eventually, I solved it by creating a new file altogether.  What I was doing is that I had cross a part of the picture over the whiteboard square and this mysterious bug happened. Yet when I attempted to do something like that at other times, I hadn't had the same problem. 

So, I wonder what can possibly be the problem? Do you think I just have to start over like I had been doing or I should reinstall it? Is there really a possible effective solution to this odd issue? 

 Thanks.

[John Waller]

Which Adobe software are you using?

[Beverly5E9A]

Adobe Illustrator 2021 

[pixxxelschubser]

One question:

Was the menu: View --> Trim View  active in these cases?

[Beverly5E9A]

What do you mean? How can it be involved in this bug problem?

[pixxxelschubser]

Maybe I misunderstood your question:

… while doing college assignments the current layers, for some unclear reason, became invisible. I tried to try to solve it or make it visible again … What I was doing is that I had cross a part of the picture over the whiteboard square and this mysterious bug happened …

By @Beverly5E9A

If so, then describe a bit more in detail with screenshots before and after.