Edit: The patch appears to have solved achievement issues.
WARNING: Taking the FREE map from lupo in Willow's End appears to void this, since it has a spirit light "cost" (even though it is zero).
The patch to fix achievements has been released. However, it disables fast travel from the map without purchasing the ability, which *could* impact trying to combine lightless, shardless, and look at the time (speedrun). However, I do firmly believe you can speedrun the game in under four hours without fast-travel from map. My speedrun using this feature was 2h20min. Not being able to fast travel at any time wouldnt add more than another hour to my run. I *believe* you can still fast travel from spirit well to spirit well without buying this, as well. Just not from anywhere. A user below already did a 3h20min run without buying the fast travel upgrade.
For this one, do not spend ANY spirit light. Not just at shops, even buying a map will void it. And anytime you buy something the game saves so just avoid talking to any sellers at all.