I could reproduce this with a signed email. There was already a ticket for it where I just added some logs so hopefully the developers can find out what the cause is.
Your thread is not a duplicate since the mentioned ticket was created on dev.gnupg.org which is a ticket system for Gpg4win and GnuPG so it’s something different Right now it isn’t solved and because the developers have much to do I cannot say when someone will be working on it.
Thank you for telling me that.
PS:I’m trying this on my working PC (Outlook 2019), and it seems nothing happened until now, and I’ll try it for a long time to see.