You haven't by chance got "Filename uses: Timeline name" selected, have you?
Otherwise, it works for me on 16.1b3
V16_1RenderFilename.jpg (70.72 KiB) Viewed 448 times
Resolve Studio 17.4.6 - Fusion Studio 17.2.2 - Windows 10 Gigabyte GTX1080ti 11GB - AMD 1950X - 64GB 2400 Gigabyte X399 AORUS Gaming 7 Intensity Pro 4k Presonus 192 Audio Interface Separate M.2 SSDs for OS and Resolve Cache