The extra stop would matter if DNV wasn't the driver. Maybe the last time he saw her she WAS getting in her vehicle, just not at the Shell station. If they stopped along the way that's ample opportunity for someone else to get into her car if no one else was with her leaving Dublins.
I just question whether she was actually the driver of her car during the entire, or any, of the post-Dublins time period. Im not saying she wasn't, I'm just saying I don't think we can safely assume someone from another vehicle caused the GPS to stop functioning when there has been no confirmed statements that anyone, DW included, exited (or didn't exit) their vehicles at the Shell.
It also matters what time they left, if they left at 10:45 or later it's reasonable to assume they didn't stop before the Shell and it took 20 minutes to get there- maybe they hit some red lights. If he is only Car 1 and not Car 3, he leaves at 11:07- 30 minutes later he texts MK and says he's at Dublins getting the phone and lost her long the way. That to me says he just got there and was letting the others know what was going on. If he was both Car 1 and Car 3, he hauled ass back to Dublin's to make it the in half the time or he lied about being at Dublins at 11:37. In which case makes his entire statement, as told by family, unreliable.