One of the change in u-boot v2020.04 was the enablement of HDMI in u-boot.
I tested this scenario while upgrading u-boot with WQHD Dell u2719d which I have access to and it was working.
However since the switch to u-boot v2020.04 there are two reported cases already that users cannot boot with v20.05.x and HDMI cable connected during boot.
Unplugging HDMI cable for boot and plugging it after boot helps.
Images are getting rebuild - from trunk with 20.05.6 version. Its too complicated to build from 20.05 branch …