The logging page in the admin UI has a "Core" column, but there is never anything in that column. I fired up the techproducts example, then used the Documents tab to try to index a document missing the "id" field, and got this error in the logfile:
ERROR - 2018-04-18 18:51:31.232; [ x:techproducts] org.apache.solr.common.SolrException; org.apache.solr.common.SolrException: Document is missing mandatory uniqueKey field: id
The core name (techproducts) is in the logfile as seen above, but when looking at the logging page in the UI, it can't be found anywhere.
This is the case in both master and branch_7x. I also tried it on the 6.6.3 version (binary package) with the same results. On version 5.3.2-SNAPSHOT, the Core column says "null" for all logs, instead of being blank. That column does not appear to be present in 4.x versions.