Hi
I had the same issue with a S912 (Beelink GT1 Ultimate) and a Sony X900F, after a power outage the box booted quicker than the TV and was set to 480p.
I ran “cat /sys/class/amhdmitx/amhdmitx0/disp_cap > /storage/.kodi/userdata/disp_cap” and edited /storage/.kodi/userdata/disp_cap to remove the unneeded modes and put 1080p60 on first line.