Hello, thank you for the suggestion, I just reflashed the same build ( LibreELEC-n200-AP6330_2G.arm-9.2.8.8.img.gz ) replacing the .dtb file you linked as: dtb.img and also kernel.img file; still no boot from sd card or usb.
The v3.10-based legacy kernel does not care about dtb.img, it only cares about the one integrated in the kernel.img file. So, it is unnecessary to exchange dtbs under the old kernel, because it will have no effect. In addition, the Meson8* devices cannot boot the OS from an USB drive, so it is worth trying only from an SD card.
The aml_autoscript under each version also differs, so if you do not use the toothpick method, it is not certain that it will boot. LE10 test versions are not compatible with the old 9.x. So you may have 2GB of RAM, but if you did the toothpick with the LE10, you have to do it again for the 9.x version. (And vice-versa...)
How much memory does the working LE10 show? (Due to the root squashfs filesystem unpacked into the memory, it will be less, so if there is around 1.5 GB, you actually have 2 GB RAM in your box.)