get_user_meta and umeta_id

You can fix this in 1 of 2 ways:

1. change the call to add_user_meta() to update_user_meta() when your 1st conditional evals to true. As explained in update_user_meta(), “If the meta field for the user does not exist, it will be added.”
2. pass true as the $unique (4th) param to add_user_meta(). As explained in add_user_meta(), the $unique param controls “whether the same key should not be added” (i.e., when true, if the meta already exists, another one will not be added; it defaults to false).

In most cases, which is preferred comes down to “style”.

Edit

The same applies to add_post_meta() vs update_post_meta() and add_term_meta() vs update_post_meta().

Where #1 or #2 matters is if you’ve hooked into update_{$meta_type}_meta and expect it to always fire. In case #1 (i.e., always use update_user_meta()) the update_user_meta action will not fire if the meta does not already exist, since update_user_meta() will simply call add_user_meta() if the meta doesn’t ready exist.

Hence, if you care about capturing meta additions, you should generally hook into both update_{$meta_type}_meta and add_{$meta_type}_meta, even if you always use update_user_meta().