Why are there gaps in my object? I would like to know what went wrong here. I'm learning with tutorials and it seems I did something different.

When I started sculpting it appeared that there is a gap without texture around the top. I do not have the gap problem on the second picture because there are the 2 holes missing on the upper side. For the holes I did it with separate loop cuts and then extruded and again some loop cuts for smoothing the edges.

But why do I have the gap? Can anyone tell me what I did wrong?
I think it has to do with the sculpting engine. What is happening is the faces are being smoothed or deflated, etc. (basically shrunk) and one will go into another. you can see this if you deflate a default sphere or something. To fix it, smooth, inflate, flatten until it appears to be fixed again.