The save button is the first icon in the toolbar. It therefore appears very close to the edge of the screen when the window is maximised. There, the mapping between touch and screen is rather non-linear for my screen (I suspect this is a general feature). This means, I often miss the icon and hit nothing instead. Of course, I can try again, and again, but due to the non-linear mapping, I might easily hit some other icon. The trouble is that I never know whether the save operation was performed (at least once) since it is not indicated.
I have no unique suggestion to resolve the problem. Some solutions come to mind:
workaround: use the file menu instead