A straight line?

That often indicates that Strava/Phone has crashed or was turned off, and recovered from the crash. So it connects the known points with a straight line.

So, for example, a couple of days ago, I stopped at one store. I apparently jostled my phone in the pack, and it shut off. Then at the next store I jostled it again, and it restarted.

Thus, for that ride, it shows the whole loop, but a straight line for the section between the two stores.

Do you have a handlebar mount for your phone?

I tend to like to keep Strava running in the background on my phone. So, should the phone screen get activated when I'm not aware, it takes a couple of button clicks for Strava to pop up.