ESW stands for Entry, Section, and Word anchor. In your case idx could not find a corresponding matching term, and the neighboring words of the old position no longer matched. With the new anchoring the position is correct, the term has still not been found. But it does not have to be, if not only keywords from the text were used. If the entry is correct, just leave it, it will disappear the next time you open or export it.
Color Coding
E:
Green – matching entry found
Red – no matching entry found
S:
Green – section found
Red – section not found
W Top:
Green – both anchor words were found
Orange – one anchor word not found
Red – neither anchor word found
W Bottom:
Green – word position unchanged
Orange – word position in relation to beginning of section changed by up to 10 words
Red – word position in relation to beginning of section changed by more than 10 words