With 足並みが揃う approved this is really not needed.

See Instead: 足並みが揃う　足並みを揃える

Started because I didn't think this gloss matched very well, then discovered that there was already a better entry in the affirmative. 

Essentially, even if the negative might be a little more popular, it is still redundant.

This isn't "failing to reach an agreement". It's "failing to get on the same page", maybe "failing to see eye to eye", "failing to work in unison".  If you like any of these, I think they should be added on the main entries 足並みが揃う and 足並みを揃える。

From the earlier reference: "lack of concerted action among the strikers", "concerted" was the key term. "to act in concert" .  The strikers are failing to work as a cohesive group to attain their goals (they are disorganized, they don't agree on demands, etc...)

Because these are ordinary verb structures, the alternative is to add every negated variant of note:
足並みを揃えない	353	5.5%
足並みをそろえない	240	3.7%

足並みを揃えず	58	0.9%
足並みをそろえず	24	0.4%

足並みが揃わない	2278	35.4%
足並みがそろわない	1517	23.6%

足並みが揃わず	1194	18.5%
足並みがそろわず	745	11.6%

足並みがそろわぬ	30	0.5%

GG5 example: スト参加者たちの足並みがそろわない． There is lack of concerted action among the strikers

oops

@@ -15,1 +15,1 @@
-<gloss>failing to reach an argument</gloss>
+<gloss>failing to reach an agreement</gloss>

eij
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