Our current islandora_solr_islandora_basic_collection_backend_callable (Solr driven collection display) uses query (q) to pass a Boolean query
This set of OR query statements (which can never in a sane islandora installation) conflict with settings you can define in your solrconfig.xml file to force things like minimum match to be 100%.
If you Solrconfig, for your default query handler has something like
which means, make all optional statements required and make sure they all match and always use AND, collection display breaks (0 results). Moving mm to 90% allows the display to work, sadly breaking the needed functionality of having all query words (when dealing with user input) to match.
Solution is to move our query to a fq (filter) as we do in most of Islandora's query functionality when dealing with programmed conditions or ones that could depend on alternatives, missing alternatives. (OR)
I think there are many other ways of breaking the q= when dealing with custom defaults at solrconfig level, so moving to fq seems a safer and proven approach.