android: how to clear restrictive permissions on internalSD
not really an answer, but i ended up resolving the issue by reformatting the data partition on the phone and restoring the data on to it with the help of TWRP. the wrong permission / dead symlink / whatnot got removed and was not present in the TWRP backup.

this thread pointed me there:
https://forum.xda-developers.com/g5/help/please-xt1675-stock-fastbboot-firmware-t3692083/page2#post74872938