Hi,
I have replicated your issue in my environment. It might be known issue of Microsoft IME in recent Windows update. There is still a known issue when using the Microsoft Japanese Input Method Editor (IME) even in the latest Window update January 12, 2021—KB4598242 (OS Builds 19041.746 and 19042.746)
Below article list some issues when using Microsoft IMEs and also provids some workarounds. Maybe you can have a try.
https://support.microsoft.com/en-us/help/4564002/you-might-have-issues-on-windows-10-version-20h2-and-windows-10-versio
Thanks,
Eleven
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