Searching is considerably different in the latest development versions that use Lucene syntax and there is work going on to make the transition less disruptive. The Lucene syntax also affects search-groups, so you may find entries missing from search-groups that previously worked. The groups are converted during upgrade but some groups may need manual adjustment due to some fundamental differences in the search functionality.
All your groups are defined at the bottom of the .bib file, so if you are not sure which groups contain search syntax, you can find them easily in the .bib file, rather than checking one by one in the GUI.
To search for an author using the latest syntax use the form author:Esteelpaz
Also note that until recently JabRef imported PMIDs from XML data (references collected via the browser extension or online searches in JabRef) but did not import PMIDs from PubMed text files. Missing PMIDs baffled me for a long time until I finally realised this and at my request the maintainers promptly changed the importer.