I have been experiencing the same problem -- invisible text that I type in OneNote 365, for maybe two weeks. Here are some specifics:
* When I switch from another window to give OneNote the focus, I click somewhere and start typing, but the type is invisible. If I click on another OneNote tab, and then back to the original tab, the text that I typed shows up, and allows me to proceed
normally. It won't happen again until I switch to another app (such as Internet Explorer) for a while and then go back to OneNote.
* I've been using OneNote for a couple of years in this exact environment, and the only thing I can think of that's changed is that I upgraded from Office 365 Small Business to Office 365 Business about when this started happening. It seems like the bug
was introduced in that version, because it never happened before that upgrade. I do not see this problem in any other app.
* I'm using the desktop version of Office 365 Business version 1720 build 7870.2024.
* I had this problem on Win 7 Pro, and today upgraded my machine to Win 10, but the problem persists.
* I have two side-by-side monitors and this problem seems to happen when OneNote is on the left/secondary monitor. But this fact may not be relevant.
* I have not noticed any other odd behavior in OneNote or in any of my other apps including the full Office suite.