Working ILS with No Diamond

GS captured and tracking, but no GS indicator. What’s going on?

Not sure, what aircraft is this?

Cessna 172 or c400.

Hi @ImXLXL
I’m not seeing any issue in the stock 172/G1000 doing an ILS into KSTL in an unmodded sim.
VNAV down to GS intercept altitude (per chart) with LOC and GS armed with APR button:

Then the LOC locked and the GS diamond moved down to where the plane caught it and flew ILS down to DA.

Have you tried with any mods/add-on’s/etc removed?
Regards