Are you using the SimVIm currently? If so, wait until next update.
Or, probably you use deprecated functions in the data.cfg file related to some "modes".?
1). As for XPDR mode that you need to display (current mode in same display position),
you should use the "XPDR_Msg" only parameter, no more:
Find it in the "generic" XPDR map (first picture in the map:
OR (best way):
1). You can simply select the transponder type KT-73 in the image map configurator and assign display to 8-digit indicator (XPDR_Code).
In that case you will get fully working (as real) transponder KT-73 with all its work logic accordingly with its specification.
Here you can see how it should work (select interactive map in transponder): https://simvim.com/svc_custom_radio.html