GPS on phone apps are always a crapshoot.
To save bandwidth and power, the ‘tracking’ is fairly granular, so the points aren’t super close together, so if you make a couple turns really close together, like your cul-de-sac u-turn, it may not capture the whole thing
Even though your phone has a GPS chip, it still tries to go off cell tower triangulation, so most apps aren’t ‘true’ GPS. In addition, many of the map-based apps try to force your track onto the street map; I’ve had times (running) where spotty signal had my track bouncing back an forth between two adjacent streets, making my pace 2-3 times faster than it should have been, over that stretch b
Finally, I’ve found that some phones are better than others; my old HTCs were very good, and my IPhone 4 was pretty reliable, but the l6 and 8 I have now were very particular; they need good weather and certain cases/holders to have reliable routes tracking.