To ease usage to a wide range of people, php My Admin is being translated into 72 languages and supports both LTR and RTL languages.
Consequently, change the ownership to that user or add write access for all users. I had this same problem on Ubuntu 18.04 when I replaced the php My Admin version from the package repository (v4.6.6) with the latest version (4.8.0).
I don't know if you are running on Ubuntu, but maybe my response will be helpful to you (or others) who encounter something similar.
php My Admin is a free opensource software which helps user to manage/administrate of My SQL database in Web which was writen in PHP.
It supports wide range of operations on My SQL, Maria DB.
I agree with the others that I'm not aware of any unfixed security issues in 5.5; in fact as dartonw mentioned since 5.1 is nearing the end of life they won't be fixing any vulnerabilities found in that, so you'll need to upgrade sometime.