There is a patch: https://sourceforge.net/p/taskcoach/bugs/1593/ works for me
+1 - same here with Xubuntu 18.04
In my case it was a problem for gpg-agent to connect via pcsc to the gpg smartcard (Yubikey) - installing apt-get install pcscd scdaemon gnupg2 pcsc-tools and restarting /reconnecting the agent found the keys on the card Otherwise remove the ssb marked stubs from the keyring