Hi John,
there was indeed an error “[ERROR] Missing system table mysql.proxies_priv; please run mysql_upgrade to create it” in the logfile, and mysql_upgrade seems to have fixed that.
But unfortunately the import error stays the same 
Some more information:
Trying to import from server A to server B.
Server a is running mySQL 5.5.54 and Centos 6.9
Server B is running 10.1.23-MariaDB and Centos 7.3 (this is my testbed for new stuff. I wanna see, if these things are ready for production)
Cheers,
Michael