I experience this too and, like you, Excel starts off fine and then will freeze up after finishing entering text into one of the cells. For me there is a kind-of workaround.
When I type into a cell and then nothing responds, I move away to another program, Mozilla for example, then go Alt Tab back to Excel and the sheet responds to key presses / typing again. That doesn't mean it won't freeze up again after entering the next cell data, requiring another Alt Tab move away from Excel and then back to Excel again.
I hve not been able to figure out what causes this, and why, once it has started responding properly again, it works fine for a few more entries and then ties up again. Sometimes it seems to occur when Excel auto-formats something like a date, but tonight my date inputs are all working fine.
I'll pay more attention when I do some more work (I've a couple of edits I need to make this evening and a couple more entries I need to add, so if any of those freeze Excel I'll take more notes).
I'm using Excel 2016 on Win10 and with NVDA 2018.1