Based on the info about this being caused by the added support of PIV, I poked around on the docs at https://gnupg.org/documentation/manuals/gnupg/gpg_002dcard.html and noticed the disable-application stuff. I added "disable-application piv" to ~/.gnupg/scdaemon.conf and the behavior went back to pin caching working as before. Since I don't use PIV, this is an acceptable workaround for me.