I had seen a few posts about incorrect display of numbers in various systems. I guess I am experiencing the same thing. If I dive into my crowd sim I can see all 6 agents correctly numbered. When I go up one level to OBJ the numbering changes and I no longer see the correct numbering. I do have two groups of agents, red and green so it looks like the numbering is being reset when a new group is processed.

Is this correct? I actually expected to see my particle/agent index instead of a participant in group index.

The viewport has different sets of display options at the scene level vs the geometry level. So it's really hard to say unless you have a scene that reproduces. Or you can try renaming your houdini15.0 folder to something else prior to starting Houdini to reset your preferences and see if that helps.