Unposted AR Write off and Adjustment

We have a difference between the AR Ageing and the GL balance. We think we tracked it to an AR Adjustment that does not seem to be posted to the GL. Two calls to support offer me different fixes, but no explanation on how an adjustment entry is not posting.
Anyone seen this before?

I’ve seen it when the account called out on the adjustment is the actual AR account. That essentially posts to the AR detail but not to the GL because the journal entry to AR nets out.

I am not sure if that is what I have. I will see if her instructions actually provide the accounts to use. What I have is a posted cash header with some of the associated cash detail records unposted.