tftpd allows connections, but times out transferring a file
Seems you're starting tftpd-hpa from xinetd and as a standalone service at the same time. Please choose one and disable the other.
E.g. set disable = yes
in /etc/xinetd.d/tftp
and restart xinetd.
Then restart the standalone service service tftpd-hpa restart
and try the connection again.