While the connection history initially displays correctly, any queries against the history fail with the following error:
This is due to the use of the POSITION() function within the query and is presumably a holdover from the initial creation of SQL Server support for Guacamole. This function is present in both the MySQL and PostgreSQL flavors of the Guacamole history query, which predate SQL Server support and would have been used as its basis.
Unlike MySQL and PostgreSQL, SQL Server does not support the POSITION() function. The CHARINDEX() function should be used instead.