I’ve reported this on the GnuPG bug tracker, but given that GPG4WIN seems to be somewhat separate I figured I’d post it here as well.
The root cause of the problem seems to lie in gnupg 2.3.x somewhere as rolling back to 2.2.33 appears to resolve the problem.
I have the same issue on Windows 10.
suggested “workaround” to not set a smartcard port doesn’t work for me.
Only thing that works is to force-kill the scdaemon.
I didn’t downgrade gnupg.
I’ve noticed it hangs for a little bit when (re)loading the certificate cache when starting Kleopatra a while ago. In my observation it seems to take longer based on how long ago you used the program.
Hi Mark,
you maybe seeing something else, if it works for your at all. 
There are several potential reasons why it may take more time,
even legitimate one. If that is an issue for you, please open a new discussion topic.
Hi Kim, thanks for your feedback, I’ve added it to https://dev.gnupg.org/T5760
Best Regards
Bernhard