Issue also seems to occurs with 7.1.1 (`dmesg -f kern` output attached).

The DisplayPort to HDMI dongle does not have markings on the body to 
identify the exact model, but by the looks of it I think it might be a 
Vention HBKB0, which seems to be marketed as "1080p@60", "DP male to 
HDMI female", "classic" (as opposed to "4K"). According to some 
materials, the chip inside is a MXP3361.

The text on the HDMI cable reads "ULTRA HIGH SPEED HDMI™ CABLE - 
WWW.HAMA.COM - HAMA GMBH & CO KG 86652 MONHEIM/GERMANY - 82623".