I created a custom tag %VOCALS% to display who the singer is for a specific song. After going through some issues I noticed that if that field has multiple values the \\ separator does not show up under that tag, causing me to think that there is missing information. I already went through and probably messed up my library adding back information to one of the now known two fields.
EDIT: I fixed the issue and found out more about how this works. changed the field to $meta_sep(vocals,\\)
This can be marked as no bug.