"...We are being told this is wrong."

Being told by ???? that it is wrong?

"It does not show in box 10, section 1231 gain/loss. We are being told this is wrong."

Did you do your own research?

Such as this article:

https://www.investopedia.com/terms/s/section-1231.asp

We are being told it is wrong by a CPA 

Yes. I've seen this article.  Thank you. 😊

"Yes. I've seen this article."

Then the question remains: Do You think it is wrong? You're the professional tax preparer.

Did you read what the IRS tells you:

https://www.irs.gov/publications/p544#en_US_2020_publink100072478

"...You're the professional tax preparer."

Maybe, maybe not... I'm not convinced.