Hi guy
https://mega.nz/folder/QnAVkYbJ#lTmIeHsGZtbjnx4HySALYA
i compiled stable 21.02.0 for MR6400v3... you can try this firmware...
i add few line in qmi.sh & qmi.js... Add script for WAN & SIGNAL STRENGTH led
Don't forget to reboot after finish flashing...
let me know if it working...
Thank You