rTSS in Training Peaks is calculated off of threshold pace rather than HR. If that is set too slow, that would also give you higher than realistic TSS. hrTSS is a separate calculation based off of threshold HR. And then TSS (for running) is calculated based off of running FTP if you have a Stryd or another power meter.
On TrainingPeaks, you can toggle between TSS calculations by going to the little drop down arrow next to the TSS box in the pop up window you get when you select the workout.