Certain settings combinations always fail on 0.7-dev and it's unclear why. It seems to have to do with the AccessDHC helper when it doesn't have any item requirements, which hints at potential issues with many other helpers, too.

Settings string to reproduce: NlgC5VAAQQgAeWFAEAQAAgAAAAQAAAgAQAAAAAAgABAAAAAAQAQAAAAAAAAAAAQAAgAAFB4=
The issue is that it can't place DHC Small Keys, likely because it thinks you can't access DHC.
This only happens when no element, sword, dungeon or figurine requirement is set. Enable either one and it works.
Set DHC to "Always Open" and it works again. Set it to "Never Open" and it fails again, but now with a "Randomization succeeded, but could not beat Vaati!" error. Again, only with no requirements.

It seems to have something to do with this line:
AccessDHC; Helper;; Helpers.GOTSWORDS GOTELEMENTS DHC_FIG DHC_AD
The issues arise if these 3 defines are all empty and the GOTSWORD helper is empty.
If you add some item requirement to the AccessDHC helper, it also generates.

From what I can tell, these issues were probably introduced with the recent caching changes.