Why sometimes do I get a Track AND an Activity? And others only a Track?

A track is a traditional GPS file, and an activity is a Garmin fitness watch file. Your device likely has a setting that allows you to choose which file type you want, including both types.

All I do is select Start Tracking, Stop Tracking.  I do it the same way everytime. I don't understand why I sometimes get a Track AND an Activity? And other times only a Track. It doesnt make sense to me.  I have an InReach and no other devices. 

I am making the assumption that "track" here means a real-time track transmitted via the Iridium satellite network. And that activity is a more detailed record of your path which remains on the unit until you sync.

You do not specify the type of unit, so I can only talk about this in general terms.

In theory, these two things are entirely independent of one another. That is, you should be able to send iR track points without recording an activity. You should be able to record an activity without sending track points. Or you should be able to do both at the same time. In theory.

In practice, there has historically been some coupling (both intended and unintended) between the two. That is, starting one thing sometimes strts the other. Or not. Stopping one thing sometimes stops the other. Or not. Let's not even talk about pausing.

On some of the latest devices, you can intentionally tie them together.

For my part, I ALWAYS check "both sides" (sending and recording) every time I make a change from either side. If I have to make a change on the "other" side to get what I want, then I check both sides again. Yes, painful. 

The whole thing is buggy. It's a result of Garmin attempting to bring iR devices fully into the Garmin handheld universe. This kind of thing did not happen on older devices where "sent points" and "logged points" were truly independent. As soon as Garmin tried to "intelligently" connect real-time Iridium tracking with activity recording, things went sideways.

inReach is a feature associated with a device. Do you have a GPSMAP 67i, or a Mini, or a Montana 750i?  For each device the "I" means inReach functionality associated with that device. There is no inReach device, only a device which incorporates inReach.

The device will have a setup menu of some sort, which will determine the file type. I have a GPSMAP 66i and I can choose to just record an activity or an activity and a track.

Are you talking about Setup > Recording > Advanced Setup > Output Format?

Setup > Tracking > Link with Recording?

Tracking > Start Tracking vs. Recording Controls > Start?

Something else?

The reason I ask is your reference to "file type". That suggests Output Format above. That really only applies to "activities". Nothing to do with sent points (iR "tracking"). This was Garmin's response to the fact that .fit is a proprietary Garmin format. Whereas .gpx is usable by virtually every GPS device and every type of mapping software.

Garmin differentiates between "Tracking" and "Tracks". The original commenter didn't mention Tracking, only Tracks.  Since Activities and Tracks essentially contain the same data, I again assume he is referring to Tracks, not Tracking.

Let me clarify.

I have a Garmin Inreach Mini2.

I select: Start Tracking

Sometimes this produces an Activity AND a Track

Sometimes only a Track

I have no idea why.