do you already had read this articel on how to troubleshooting performance issues with tempdb?
1.) they recommend to use the latest version of SQL Server 2017 ;-)
2.) You already followed the recommendations regarding 8 datafiles for the tempdb, but maybe you should increase them.
3.) Or consider upgrading to SQL 2019, as that version has an big improvement for tempdb page contention.
I hope my answer is helpful to you,
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