Today it crashed again. I can see some strange lines in the log an hour before importing:
2019-02-11 06:57:49 RT --------------------- backtrace end --------------------------
2019-02-11 06:57:49 RT 25: hansa-autoserver-37018218() [0x406bc1]
2019-02-11 06:57:49 RT 24: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0) [0x7f00426ac830]
2019-02-11 06:57:49 RT 23: hansa-autoserver-37018218() [0x406b24]