Gathering Echoes | Main Story

When you return to a location after some time (e.g. Talos I Lobby) you can encounter new enemies, usually more powerful than the previously defeated ones

Yes, enemies in Prey do respawn and when you go back to a location you can encounter new enemies even if, during your last visit, you cleared an entire location. Here are the most important information about this game mechanic:

1. Respawns don't work in a way that a defeated monster or a machine is replaced by the same enemy. The game scales the level of threat to your current progress in the main story. For example, when you go back to Talos I Lobby in the middle of the campaign, instead of facing weaker Mimics and Phantoms, you can face Greater Mimics, Etheric Phantoms or even a Typhon called Nightmare.
2. The biggest chance for enemies to respawn is when you return to a location after completing some main or side quests that took place in other area.
3. A respawn can also occur when you didn't explore a location for a longer period of time. Enemies respawn even if you haven't made any progress in the main story or in side quests.

How to deal with a problem of respawning enemies? Here you can find a few tips:

1. If you play on easy or medium difficulty then respawns shouldn't be a problem, especially because most of the enemies leave valuable items or junk which can be placed in recyclers. Because of the lower difficulty level you don't have to avoid fighting them. Instead, you can try to clear the locations again.
2. If you play on hard or Nightmare difficulty then enemy respawns may cause you problems. Each new battle creates a chance that your character can die or, which is as important, you can deplete your ammo, psi hypos or medkits. Here, fighting with enemies is not recommended and you should focus on avoiding conflicts.
3. Avoiding "respawned" enemies should be easy for you because when you return to a location you know how the rooms are placed etc. If it's possible you can use detours or decide to use sprint (however, running may not work against faster Typhons). Remember that the game allows you to save your game and that you can use passages to other areas even if you are attacked or wanted.
4. Try to limit your travels between different areas (those, that are separated by loading screens). For example, if you received a side quest in which you must return to a certain location you should postpone that and go there when you have to complete other missions in that location (the exception to that are time-limited missions that can be failed).
5. Try to get, as fast as you can, plans that allow you to make ammo, medkits and other items useful in combat . Having them reduces a problem where you can use all of your supplies during a fight which means that you have to stop using, e.g. a given type of weapon until you find ammo.

Warning - If you plan on spending a lot of neuromods on alien abilities then you can use respawns as an opportunity that allows you to perform missing scans. It is especially useful when you missed your chance for an easy scan during your first encounters with unknown types of Typhons.