I have same problem.
I don't know why, but resolved it removing special permission attributes of mongod.conf file, put the own of file to 999:999 (mongodb user in container) and chmod 644 to file.
I hope this is useful for you.
[/share/apps/mongo/conf] # ll
total 32K
drwxrwxrwx 2 999 999 4.0K 2021-02-01 12:00 ./
drwxrwxrwx 6 admin administrators 4.0K 2021-02-01 11:43 ../
-rwxrwx--- 1 Jose everyone 645 2021-02-01 12:00 mongod.conf*
-rw-rw---- 1 999 999 348 2021-02-01 11:27 readme.txt
[/share/apps/mongo/conf] # cat mongod.conf > mongod.conf2
[/share/apps/mongo/conf] # rm mongod.conf
[/share/apps/mongo/conf] # mv mongod.conf2 mongod.conf
[/share/apps/mongo/conf] # chown 999:999 mongod.conf
[/share/apps/mongo/conf] # ll
total 32K
drwxrwxrwx 2 999 999 4.0K 2021-02-01 12:02 ./
drwxrwxrwx 6 admin administrators 4.0K 2021-02-01 11:43 ../
-rw-rw---- 1 999 999 645 2021-02-01 12:01 mongod.conf
-rw-rw---- 1 999 999 348 2021-02-01 11:27 readme.txt
