Thanks very much for the reply, and that certainly does clear things up!
Please allow me to elaborate on the quote you referenced. I prefer to navigate in the heading follow mode, and I was hoping the lock feature would allow me to set this as my default mode. the original (paid) Groundspeak app defaulted to this mode, and it is the only feature I miss from that Groundspeak app.
Currently, once I click on "Navigate to Cache" the arrow head icon in the lower right screen is pointed in the 1 o'clock position, and appears as a white arrow outlined in green. From there I click once, at which time the arrow becomes solid green, remains in the 1 o'clock position, and zooms in on my current position, with a red line showing the navigation path (cache is not visible on screen until I approach it). I then click the arrow head a 3rd time, at which point it becomes a solid green arrow head with a green vertical line (forming an arrow), and is in the 12 o'clock position - the "heading follow" mode. Each time I pinch zoom in/out and/or change to a new cache, I have to go through this process to re-enable the "heading follow" mode. I did not see an option in settings to set the default navigation mode, which is the "missing" feature I was referring to. To illustrate, I have attached a labeled screen shot for reference.
Thanks for inquiring and considering!