This sounds a lot like this unsolved bug:
However, doing a handful things at once like a major upgrade of a system (from 5.1 to 6.0) plus upgrading a quite complex mod (like Xposed) sounds like a terrible idea. You may want to split this into several subtasks after each one you can assure your system boots and works, and if not, isolate better your problem. Here is how I’d do it:
- Uninstall Xposed.
- Boot into your clean system and upgrade to Marshmallow
- Boot into Marshmallow and make sure everything works as expected (if not, refer to the bug linked on the top)
- Install Xposed Framework for Marshmallow (SDK 23)