When attempting to add a long query (over 255 characters) to the "work sub-filter" on the "General" configuration screen for a Kanban board and click update you will get a general error message come up and it will not let you save. If you then check the catalina.out file you will find a long error message in which is the following:

Caused by: com.mysql.jdbc.MysqlDataTruncation: Data trucation: Data too long for column 'QUERY' at row 1

To work around this issue I changed the column length of the "query" column to 2000 characters and this worked around the issue successfully.

Workaround :
Create a saved query with the JQL you want to use in the work sub-filter and reference that saved query from within the work sub-filter