My display problem have been solved now by connecting monitor by HDMI cable and DisplayPort/HDMI converter to HDMI-2 port. This with kernel Linux ci547 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2 (2019-08-28) x86_64 GNU/Linux
Using HDMI cable on DP-1 port make drm issue "Link Training Unsuccessful" messages. On kernel 4.9.0-9 I had no problem getting 1920x1080 on DP-1. ZOTAC ZI547 have 2 output ports, 1 DisplayPort (HDMI-2) and 1 HDMI (DP-1).
