Issue using file descriptor assigned file resides in /tmp

[Budi]

Anyone experienced too:
Bash cannot use file descriptor assigned file that resides in /tmp  ?
i.e. inside script:
...
exec 3< <(/tmp/dls1)

while read -r -u3 f1; read -r f2
do
 # ...
done < <(cat /tmp/dls2)
...


output:
...

bash: /tmp/dls1: Permission denied

While second file read into f2 works. Please advise the wisest solution.