first notice that its not turning frequently location on would help your Iphone to collect more data about the locations you visit. its kind of dosnt have a background reffreshing . so it will be more accurate to let your device learn about your most visted locations by using the APPLE MAP .
while apple map is on and you driving . the iphone will force the phone to save cutch of all this street names you may go throw. (spically IPHONE 5 & 5s) . and APPLE MAP dosnt work as good as any othrt reagion . i mean the names of placed and streets is very depend on you iphone or your location region. sometimes yes the mini picture if that place you been to or the name even would disappear. that could be happen in case of many reasons. its a data was only saved in your phone and lost except the date and time of the visiting may be the only to appear. that could be for any of reason of delete and old backup, reste newtwork settings ( as well it cause change your iphone name back to the defult which is "IPHONE " on icloud . in case if did give you phone a name actually using setting. about... etc. anyway you have no way to get back the names back unless and that is not a conformation. if you keep it this way and you keep visit those places again and again. my advice is to reset location setting and start all over. dont worry siri still have some data saved that will help you in case if any spotlight sea