This same warning also appears if you're using positioned parameters. I have the following template:

PARSEDATETIME(CONCAT(EXTRACT(YEAR FROM ?1),'-',EXTRACT(MONTH FROM ?1),'-',EXTRACT(DAY FROM ?1),' 00:00:00'), 'yyyy-MM-dd HH:mm:ss')

which will show the error

Function template anticipated 3 arguments, but 1 arguments encountered

even though it clearly expects a single parameter (?1).

I realize this is a slightly different case, but I thought I'd mention it.

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Hibernate 5.1.5.Final