I was able to reproduce this problem by adding size only to some notches. Each value should be equal in order to maintain a non-sharped border. e.g:

/* unfocused borders*/
    .form-outline .form-control~.form-notch .form-notch-leading {
    border-top: .325rem solid #ffaabb;
    border-bottom: .325rem solid #ffaabb;
    border-left: .325rem solid #ffaabb;
} 

 .form-outline .form-control~.form-notch .form-notch-trailing {
    border-top: .325rem solid #ffaabb;
    border-right: .325rem solid #ffaabb;
    border-bottom: .325rem solid #ffaabb;
} 

 .form-outline .form-control~.form-notch .form-notch-middle {
    border-bottom: .325rem solid #ffaabb;
    border-top: .325rem solid #ffaabb;
} 

If this is not working for you, please provide me a snippet.

There's problem with it.

Those borders are being applied by its child, the form-notch element. You can modify it with CSS using selectors:

 .form-outline .form-control~.form-notch .form-notch-leading 
 .form-outline .form-control~.form-notch .form-notch-trailing 
 .form-outline .form-control~.form-notch .form-notch-middle

See how it works in this snippet: https://mdbootstrap.com/snippets/standard/m-duszak/2973948#css-tab-view

Keep coding,

Michal Duszak