A monster wants to leave the same space as an inspector. The app says it's fixated on a NPC and tries to move towards the NPC. The inspector wants to stop it by fighting it.

Can the monster just move away or does it have to make an evade check just like an inspector ?

The app gives the alternatives: 1. Attacks NPC. 2. Moves towards NPC. 3. Can't move closer. If I choose 3 the app says the monster looks for an inspector to attack instead.

I think that the logical thing would be that a monster can't just pass an inspector who tries to stop it. What do you guys think?

If the app says that the monster moves towards a specific investigator or NPC then it moves directly. Investigators cannot stop monsters during the Mythos Phase as monsters don't use evade the way that Investigators do.

While these are two separate rounds, you have to think of them as taking place at the same time. The only time evading even happens is when a player wants to scramble away from a monster in order to interact with something or run away.

Short answer, there is not much that can be done to prevent it unfortunately. You can chase it to try and kill it on the next Investigation Phase though!

Ok, thanks!