Error Msg 10314, Level 16, State 11 with SAFE assembly after upgrade to SQL Server 2017

I have a pre-SQL Server 2017 database that I restored into / upgraded to SQL Server 2017. In this database I have a SQLCLR Assembly. The Assembly is marked as SAFE since it doesn’t do anything requiring a higher level of permissions, and the database has TRUSTWORTHY disabled / OFF. The SQLCLR functions and stored procedures worked as expected before moving to SQL Server 2017, but now when I try to execute any of them I get the following error: