Hey,
After a board issue (see topic https://forum.mangoh.io/t/cannot-access-mangoh-yellow-wp7702/4848/27) I think there is a problem with the swiflash command and its -r option for recovery mode. With fw R12, this tool doesn’t work, I had to downgrade to R11 to be able to use it.
Thanks 
According to the release note of fw r12, QTI9X07-2870 is to fix userapp partition being erased which is security hole.
You might also try the following without downgrading to older version:
(Be careful of the mtd number, different FW might have different mtd number for userapp partition !!! )
root@swi-mdm9x28-wp:~# cat /proc/mtd|grep userapp -i
mtd16: 08300000 00040000 "userapp"
root@swi-mdm9x28-wp:~# pwd
/home/root
root@swi-mdm9x28-wp:~# ls
UART_Test1.wp77xx.update
root@swi-mdm9x28-wp:~# flash_eraseall /dev/mtd16
flash_eraseall has been replaced by `flash_erase <mtddev> 0 0`; please use it
Erasing 256 Kibyte @ 82c0000 -- 100 % complete
root@swi-mdm9x28-wp:~# reboot