The problem turns out to be part of the new logic that was applied to handle select (dropdown), checkbox, and radio fields. 3.1.4 had an improvement to this shortcode so that “display” values were used rather than stored values for these field types.
The flaw in this new logic is for any field type that may be displayed using the [wpmem_field] shortcode that isn’t necessarily part of the form fields in the plugin’s fields setting. This would be fields like user_login, user_registered, and any custom user meta field that is not part of the settings array.
I have reworked the logic for this function so that it will handle the new process as intended while still supporting other fields like before. This update will be released this evening as 3.1.4.1.
In the meantime, the function can be updated manually. The function is wpmem_sc_fields() in the file /inc/shortcodes.php. It begins at line 552 in the file. It can be replaced with the function here:
https://gist.github.com/butlerblog/efb97220eec309ce0897ad800fcb999f