I am building a workbench that uses spatial filters, I have several readers input to the spatial filters that have different source coordinate systems. Originally, I used the ESRI reprojector to convert everything to 3TM (EPSG: 3776) prior to the spatial filters. This included a file with a source coordinate system of WGS84 Spherical Mercator (EPSG: 3857). However, my end result is about 4 feet off of where it should be. I tried selecting a transformation (I used Pro to see which transformation they used when I used the project tool and selected that one) but the result was still the same. I performed the projection in Pro on the same file and it was successful so it was a bit confusing as to what I was missing in FME. 

I decided to instead project my other files to WGS84 Spherical Mercator and work within that coordinates system. It was successful. 

I am guessing I may be using the ESRI reprojector incorrectly, or missing an input.