Hey there, I have this mounting-problem at boot as well:
Device: MagicBox TVPC
Previously running LibreELEC-S905.arm-8.2-126.96.36.199 with gxbb_p201.dtb
Burned via dd
The default uEnv.txt is using "/dtb/amlogic/meson-gxbb-wetek-play2.dtb", which is starting, but the Remote is not working, LAN is not connecting and everything seems laggy. Since I've used "gxbb_p201.dtb" before, I expected "/dtb/amlogic/meson-gxbb-p201.dtb" to work for me, but it keeps generating the error from above.
What am I doing wrong? The SD card doesn't seem to be broken, since flashing the old LibreELEC 8.2 works perfectly.
That tvbox looks like a clone of some mecool. Try the dtb that most closely matches your tvbox.