hi @Oom_Wat and welcome! If you’re feeling social stop by and say hello!
Spatial anchors are a tricky lil fella, and it looks like you’ve tackled some of the troubleshooting as well. There are a few other things you can do that might help.
Walk around your space
This sounds a bit silly, but in order for the anchor system to be activated in Arkio the headset needs to understand your space so it can drop an anchor 
A good way of understanding this is examining how your boundary (the standard grid that Meta uses for all headsets) starts to build the mesh of your space when creating a boundary. I’ve noticed that the headset will recommend a small seat based boundary while I’m standing in a wide open space. What remedies this in Arkio is walking around your space and slowly moving your head around in order for your space to be recognized.
Check your headset for updates
Make sure to check your headset OS that it’s up to date. The Spatial Anchors API shipped a while ago and I’m guessing you probably covered this already but you never know…
Clear and reset your boundary data
In the Physical Space settings in your headset, clear your boundary data and reset a new one. I do this quite often as it’s the best way to get an accurate floor position. I’m not sure if it actually helps trigger the anchoring system, but I choose to believe it does so I can feel better about my actions.
Using the Lock Position button you can… but that brings us back to square 1.
Let me know if this helps!