SQL Server 2019 UPDATE Statement SET to function does not execute the function again for each row

Here is the scenario. I have a local SQL Server to which I have restored the live SQL Server databases. In order to be GDPR/CCPA compliant, I must anonymize the PII in the local server’s databases. I have a script to do this, and it has been working quite well when the local server is 2008 R2 or 2017. But I just installed 2019 and the same script puts the same value in every row of the table, rather than a different value for each row. It is as though the function is executed only once, then that value is used in the UPDATE statement. Perhaps it is some kind of optimization 2019 is doing? Here is a snippet of the script.

UPDATE Guest SET GuestFirstName=Utility.dbo.RANDWORD() WHERE GuestFirstName IS NOT NULL;

RANDWORD grabs a random word from a table containing approximately 100,000 English words.