Sounds like you're most likely trying to use a homestead structure. See known issues in the bug thread.

What are Homestead structures? I don't have any such mod installed.

Please refer to the pinned bug thread I mentioned.

Googling ark homestead gets you this wiki page. It is a part of the vanilla game.

https://ark.fandom.com/wiki/ARK:_Homestead#:~:text=ARK%3A%20Homestead%20is%20a%20major,rework%2C%20into%20the%20main%20game.

The symptoms you mention suggest you're trying to build with a vanilla homestead ramp/stair and it's converting on restart.

1) I did read the thread
2) They are SS not Vanilla. Everything I build, I build the SS version. And even if they were, they would have been converted the first time and thus not reset EACH time the game is restarted?

Awesome thanks for the clarification. I know I may seem patronising by asking but youd be surprised how many people say they are using the SS structures and once you drill in a little you discover that's not the case.

This is the first report I've seen of this occurring so far.

That's fair. Haven't played in years and last time I did S+ was the mod. I was aware it had ended and been folded into the base game ("in a crappier version), just didn't know that's what Homestead was.

Only thing I can think of then is these ones that keep changing are bugged. I'll try destroying them and rebuilding them.

This happened to me last night. Placed SS Wooden Stairs, rebooted the dedi server and it flipped to a ramp.