Try using multisearch. This isn't super fast, but it did the trick. I added an extra value to each list to play around with when there were multiple differences.
| multisearch
[ search source="result1.csv" NOT
[ search index="scratchpad" sourcetype="results" source="result2.csv"
| fields AVC_ID]
| eval OneNotTwo=AVC_ID
| fields OneNotTwo]
[ search source="result2.csv" NOT
[ search index="scratchpad" sourcetype="results" source="result1.csv"
| fields AVC_ID]
| eval TwoNotOne=AVC_ID
| fields TwoNotOne]
| stats values(OneNotTwo) as OneNotTwo values(TwoNotOne) as TwoNotOne
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