I have noticed this problem on PyCharm Community Edition and now on PyCharm Professional 2019.3.2 build 193.6015.41, Mac OS.
After git annotations are displayed via the context menu (right click on line numbers column), the editor's cursor disappears and the editor becomes unresponsive to keyboard input. You can still select and highlight code with the mouse, but keyboard input is switched off. The only remedy is to close and restart PyCharm.
This is an intermittent issue, as I am unable to repro after rebooting my machine. I am not certain what state is causing this issue other than the IDE has been running for many hours (or days) when this issue occurs.