 In our print layout we have two maps, we have the main map which is map 1, you can find that under the item properties and if I select the locator map it's map 2, you can see that there in the item properties. Now the scale bar should be linked to one of them and of course it needs to be linked to the main map which is in our case map 1. If I change it to map 2 you see that it changes, it uses then the scale of the locator map. So you always need to choose the correct one. The same counts for the north arrow, if you scroll down then you find there in their image rotation that it has to be synced with a map and there you can also choose between map 1 and map 2. In this case it doesn't make any difference because they are both north oriented.