Not sure what version of vbox you are using, and on what Host OS?
Only similar problem I can find, with a bit of googling, is that within vbox, this kind of problem could be caused by your ArcaOS vm settings, display, monitor count being set to anything other than 1.
You can also test a brand new install of ArcaOS (from your registered ISO) into a new vm, and don't fiddle with the vm settings too much, until you know if that new test vm has the mouse issue or not. ArcaOS comes with a set of vbox drivers built-in, so you should be able to test the issue right away.
Hope this helps ...