I've just cloned a production site into a staging environment. I copied core and contribute, cloned the repo containing custom modules and themes, cloned the database and copied the solr configuration to a new core. Bringing up the database I configured a new search server pointing to the new core, repointed the index and reindexed the site.
All my old search API Views, and all new ones I create, only show one result. However the pager can tell that there are more. Jumping to other pages works. However no content is shown. If I do a search in solr admin I get many results.
I'm at a loss for where to start looking. As far as I can see all configuration is the same in the database and in the files. Google doesn't seem to think this is a thing.
Is this likely to be a Views issue, a solr issue or a search API issue?
EDIT: I've called the URL directly as @Eugene suggested. It looks to me like only one result is returned by Solr. However as you can see it things that a larger number has been found.
Query string: http://example.com:8983/solr/core2/select?fl=item_id%2Cscore&start=0&rows=10&facet=true&facet.sort=count&facet.limit=10&facet.mincount=1&facet.missing=false&facet.field=sm_field_domains%24name&facet.field=im_field_regions&facet.field=im_field_topics&facet.field=im_field_sources&facet.field=im_field_domains&f.sm_field_domains%24name.facet.limit=50&f.im_field_regions.facet.limit=50&f.im_field_regions.facet.mincount=0&f.im_field_topics.facet.limit=50&f.im_field_sources.facet.limit=50&f.im_field_domains.facet.limit=50&f.im_field_domains.facet.mincount=0&group=true&group.main=true&group.field=ss_field_source_url%3Aurl&wt=json&json.nl=map&q.alt=%28ss_type%3A%22article%22%29%20%28bs_status%3A%22true%22%29%20%28index_id%3A%22solr_local%22%29%20%28hash%3Agpsxif%29