Please run "dmesg | paste" and share the URL, to see if there are any error messages in the log?
The one remaining experiment I can think of is writing the WP2 (not box) image to emmc. This replaces vendor u-boot with upstream u-boot and changes the early boot process. That said, I'm not sure it would resolve anything as I've not had other reports of what you're seeing and there's a growing number of users (most of whom are probably booting from SD card). I have a raw (dd) copy of the original factory image that can be restored to emmc if you wanted to put Android and vendor boot code back.
https://chewitt.libreelec.tv/testing/LibreELEC-AMLGX.arm-10.85.0-wetek-play2.img.gz
To install to emmc download the WP2 image to /storage/ and then run "emmctool w LibreELEC-AMLGX.arm-10.85.0-wetek-play2.img.gz" and it will install everything. To restore the backup, boot the WP2 image from SD card (so emmc is not in-use) and then download the backup and write it with "emmctool w backup-wp2.img.gz" .. until it eventually finishes.