Hello there People! Thank you for reading this!
I am trying to do a very basic simple thing.
I am deforming a basic square field, and I added some vegetation with Particles Hair System, calling a collection.
I want these Mushrooms Collection to just do whatever the terrain is doing.
The problem is that every time open the project they MOVE without me doing anything, I have tried many things to solve the issue, turning off rotation, etc etc but nothing is solving it. The project has no issue if the Mushrooms are facing Global Z, X, Y. the problem happens when I am trying to make these mushrooms face Normal / Normal-Tangent / Velocity-Hair.
Try it yourself, take a screenshot of the first frame, then go to a different frame, open blender again, go to the first frame. You will see the screenshots will not match.
PS: I have tried deforming the terrain with displacement in the modifier stack, and also with geometry nodes, from what I see this isn’t the cause of the problem, it has something to do with the way Normals and Particle Hair system works…
This isn’t that “big” of a problem if I will render the project on one go…but if I render 100 frames now and 100 frames later, it will be a problem where at frame 101 there will be a jump due to the change of particles… let alone if you use a render farm, or if a client wants something to change. On a render farm, each frame won’t match since they are opened by different PC and rendering different frames, so the animation will be a STUTTER MESS! If a client wants a change, then I will have to render the whole project and not just the sequence that he wants something to change.
Is this a blender problem or I am doing something horribly wrong with blender?
Here is the Blend file so you can look at it yourself. You will need 3.0 because I have displaced the terrain with Geometry nodes and not with Modifiers.
Community_[a2].blend (2.5 MB)
Much love and thank you for all the support you give to the 3D community 
