This page of the Returnal guide explains why the map can disappear and why the image on the map may be distorted. In both cases, this can make it difficult for us to properly explore the surroundings, track enemies and find 100% of the loot.
An example of a situation where the map is not available can be seen in the picture above. We cannot use either the mini-map or the large map displayed on the full screen.
The reason for the temporary lack of a map is that we found ourselves in a secret area. This can happen after we discover an entrance to a secret location or use a special consumable item that teleports Selene to a random, unknown location.
The lack of a map in a secret location is fortunately not a problem, because such places consist of a single room. We shouldn't have any trouble finding the entire loot or examining the interactive devices.
The distortion of the map can be a more serious problem (example in the picture) because the distortions happen all the time, including when travel through the main locations. It can make it difficult for us to locate unique treasures or monitor what the enemies are doing.
Image distortions can be the result of armor malfunction. This can happen, for example, if we came into contact with a malignant object.
We can try to remove the damage by performing a related action or try to do it in an alternative way, for example, by activating a proper consumable (in our example, it's the Nullification Sphere).