I have noticed that on my system (Devuan daedalus), if the flashing cursor is in a comment and I save using Ctrl-s, the cursor is no longer visible. Typing text has no effect. Neither to arrow keys, Esc, Tab, etc. Obviously this does not interfere that much with editing, since I can simply click in the main viewport to regain the cursor. It is not ideal behavior, though. I can still use the keyboard to control menus and use shortcuts (e. g. Ctrl-b toggles the boldface indicator in the toolbar), so keyboard input is not blocked or "stolen" by a process. To reproduce: 1)Create a LibreOffice Writer document using Ctrl-n or File >> New >> Text Document. 2)Open a new comment with Ctrl-Alt-C. 3)Type at least 1 character in the comment. 4)Press Ctrl-s. Your cursor will have vanished. Keyboard input in the form of typing, arrow keys, and Tab will be ignored. Expected behavior: the flashing cursor will still be visible in the comment and the user could continue typing, or press Esc to return the cursor to the document. System is i9-based home build running Devuan daedalus. I don't currently have any other systems here to test on, but I will have access to an Ubuntu system as early as tomorrow and will test there.
Tested on a mini laptop running Devuan Geronimo, LO version Version: 25.2.3.2 Build ID: 520(Build:2). Behavior is unchanged. I did find a workaround. Ctrl-F opens the find toolbar and puts the cursor in it, and the cursor then behaves normally. I hope that helps in debugging. Perhaps I should clarify that when I say "cursor" I'm referring to what I was trained to call the insertion point decades ago. I'll test on Ubuntu probably tomorrow.