You need to change the DTB file to version 5.88.190601 - 5.1.5
Located on the SD card: /boot/dtb-5.1.7-sunxi64/allwinner/sun50i-h6-orangepi-3.dtb
That fixed it for me on 5.88 dev 5.17.
Version linux-dtb-dev-sunxi64 version 5.90.190630 should work too, but I've not tested it.
I cannot post to the H6 forum so I cannot reply to @renedis with the link to download the Armbian_5.88.190601_Orangepi3_Ubuntu_bionic_dev_5.1.5 file he asked.
For him and other users that actually cannot run the Ubuntu image for Orange Pi 3 I uploaded in my OneDrive the working image: Armbian_5.88.190601_Orangepi3_Ubuntu_bionic_dev_5.1.5
PS: please can someone move to the Allwinner H6 forum? Thank you.