Thought I would post this so there is a record of the solution.
Ever since I acquired a sensor track I had a issue with it not triggering reliably when a sensor equipped locomotive passed over it.
Having some time over the holidays to fully investigate. Finally got to the bottom of the problem. Thanks to some help from forum member Albrecht.
I run a pure sine 60Hz inverter powered by a DC supply as the 50Hz UK power causes other issues with TMCC.
The issue with the sensor track is electrical noise from the DC power supply. The AC component is present on the DC output feeding the inverter.
I had a diffrent DC power supply from another project and swapped this for the existing DC supply and the sensor track triggers perfectly every time.
Next stage is to find a DC noise filter to place between the DC power supply and the inverter. For my large inverter I need one capable of taking about 100amps.