It doesn’t look to me like you’re doing anything wrong in your mappings.
Have you tried troubleshooting this from the Solr admin panel? It seems to me that if you pick a record that has multiple 035 values, you could retrieve it in Solr admin and confirm whether or not the ctrlnum field has multiple values as expected. If the values are there but the search is still failing, then perhaps it is a problem with searchspecs.yaml or some kind of more subtle Solr problem like incompatible field types being combined in a Dismax search. If the values aren’t there, then you know that there’s an import problem that needs to be investigated more closely.
Is that helpful? Let me know what you find if you still need help troubleshooting further.