Regular file cannot be written or read by root even when those permissions are set

Issue

• A file cannot be copied|read|written|removed even by root.

# cp the.file /tmp/the.file.bk
cp: cannot open ‘the.file’ for reading: Permission denied
# lsattr the.file
lsattr: Permission denied While reading flags on the.file
# rm -rf the.file
rm: cannot remove ‘the.file’: Permission denied
# file the.file
the.file: regular file, no read permission
ls -laZ the.file
-rw-r--r-- root root ?                                the.file
cat -vET the.file
cat: the.file: Permission denied