My hillclimber wouldn’t solve this until I gave it a long crib. The key consists of two words. I ran a brute force program combining the first word with every word in my list and it still didn’t find the solution. The plaintext is randomly selected from Gutenberg.org, two unrelated sentences.
DL SR YQ EH HT VC KV BG GR BY YQ UH SE UH ZC WO UA FQ ON DZ OL XN FG OU DL VD UV WO YD RH EZ HP OY RH VF ZU HT BG NL QO UC NH NO ZT AU ZF OI FC BC AT OH IV ZS AQ QO UR IO YQ EW US DL UR SB ZG FG VR PH RQ BC WR NU SU YI crib: VXDWCOXACBJLCRWPXO