This happens with arc diff as well as the web interface.
At the last step before the revision is created, there seems to be an error coming from the server:
>>>  <http> https://reviews.freebsd.org/api/differential.createrevision
<<<  <http> 456,387 us
<<<  <conduit> 456,877 us
[2018-02-10 17:18:54] EXCEPTION: (ConduitClientException) ERR-CONDUIT-CORE: Attempting to access attached data on PhabricatorRepositoryCommit (via getAudits()), but the data is not actually attached. Before accessing attachable data on an object, you must load and attach it.
Data is normally attached by calling the corresponding needX() method on the Query class when the object is loaded. You can also call the corresponding attachX() method explicitly. at [<phutil>/src/conduit/ConduitFuture.php:58]
#0 ConduitFuture::didReceiveResult(array) called at [<phutil>/src/future/FutureProxy.php:58]
#1 FutureProxy::getResult() called at [<phutil>/src/future/FutureProxy.php:35]
#2 FutureProxy::resolve() called at [<phutil>/src/conduit/ConduitClient.php:64]
#3 ConduitClient::callMethodSynchronous(string, array) called at [<arcanist>/src/workflow/ArcanistDiffWorkflow.php:588]
#4 ArcanistDiffWorkflow::run() called at [<arcanist>/scripts/arcanist.php:394]
Update: I can create a new revision as long as I don't refer to a commit in the Summary Plan (I was trying to write "rP460809").
Aha, I also ran into this, also with a linked revision in the title.