I think the issue is with the different memory modules used, my Rock64 boards is from one of the batches when the board was rather new and when 1866mhz memory modules was used even if the board spec was 1600mhz.
The old images did not have dfi/dmc ddr devfreq enabled in device tree and possible explains why you have a more stable board with the old image and problems with newer images.
The linux v5.0 image I linked to possible had the 933mhz ddr init code and that would explain why it does not work on your board, I have uploaded a linux v5.1 image with the 786mhz ddr init code: libreelec-rk3328.arm-9.1-devel-20190512071134-2f3393e-rock64.img.gz
One of my Rock64 boards:
I tried this build. HDMI is black, same as the build "LibreELEC-RK3328.arm-9.1-devel-20190416231707-c1c92b1-rock64" that I tried. I tried using SD and eMMC. Same results.
Just to reiterate. The 20181002 build still works on my board consistently. So I don't see why it can be a bad board or power supply. I am testing with 2 different power supplies, same results every test I do. I would now assume there is something different in the manufacturing of my board, as far as model/revision of chips, memory timing, etc. All I can say with certainty is that I get expected playback consistently using build 20181002 on my board. And no other builds I've tried have worked. So there is something "right" in that build that works on the version of board I have.