Solr: can not sort on multivalued field

[cyplas]

We frequently get "can not sort on multivalued field" in the solr logs:

cyp@fido /project/lindat-dspace/installation/log $ grep "ERROR.*can not sort on multivalued field" solr.log* | tail -10
solr.log.2017-06-23:2017-06-23 00:11:28,225 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.tit
solr.log.2017-06-23:2017-06-23 00:11:30,189 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.tit
solr.log.2017-06-23:2017-06-23 03:58:10,469 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.
solr.log.2017-06-23:2017-06-23 03:58:12,501 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:14,388 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:16,356 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:18,312 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:19,944 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:21,822 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.date.issued
solr.log.2017-06-23:2017-06-23 03:58:47,050 ERROR org.apache.solr.core.SolrCore  - org.apache.solr.common.SolrException: can not sort on multivalued field: dc.tit
cyp@fido /project/lindat-dspace/installation/log $

Not sure what causes this or how it affects the user.

[cyplas]

Lindat says this is probably due to some structure changes, and that a closer look at the apache logs and using a remote debugger could help.