I assume you are translating that documentMetaData JSON into some form of "actual" Alfresco properties, because otherwise that would only me indexed fulltext content, and not metadata at all.
Also, it would have been good to know HOW you are searching via the default APIs, e.g. what your queries looked like. So I only can assume that you use the literal value as a query term, i.e.
In this case, assuming the query language is fts-alfresco, there should be no error. In case you did actually run a CMIS query in the form of
SELECT * FROM cmis:document D JOIN acme:aspect A ON D.cmis:objectId = A.cmis:objectId WHERE A.cmis:clientName = 'Test$*?@!%)(_+-=~\*"\';//?.>,<'
Then I could understand the error, because in CMIS QL, there is no support for escaping an asterisk, as it is not a special character.
So, please do provide more details, or we can only guess like I did...