Comment # 1 on bug 1226042 from Ruediger Oertel

update from 15.5 to 15.6 updates gpg2 from 2.2 to 2.4 and in

man scdaemon

you can find

       --disable-ccid
              The  integrated  CCID driver for CCID compliant devices can be
available when libusb was detected at build time, and it is used to ac-
              cess the smartcard reader.  If access via PC/SC driver is needed,
please configure this option to  disable  CCID  driver  support  (if
              any).  In GnuPG 2.2, there was a fallback mechanism from CCID
driver to PC/SC driver.  The fallback mechanism worked, because scdaemon
              in GnuPG 2.2 only supported a single token/reader.  To support of
multiple tokens/readers at the same time, fallback mechanism was re-
              moved.

and as I was relying on the fallback, things broke now.