For an unknown reason (7)
I believe the answer is:
somehow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">for an unknown reason</span>' is the definition.<br/ ><span class="explanation-format__explanation">(for some reason)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for somehow that I've seen before include "One way or another" , "By hook or by crook" , "For some unspecified reason" , "In an unspecified manner" , "By unspecified means" .)