[SalesForce] Queued triggered sends in Journey Builder

Emails configured in Journey Builder are Triggered Sends, which you can find in the Interactions tab in SFMC.

You can pause the trigger corresponding to your email and download the queued subscribers or clear the queue. You can also pause and restart the trigger definition in case one email is holding up the queue.

I'm guessing there's some issue with the data coming over in the payload that isn't handled in the email scripting.

Edit

I'd revise your AMPScript to make it more fault-tolerant and to include the CustomerID which is required in the DE you're updating:

%%[

var @eid, @js, @cid

set @eid = AttributeValue("EventInstanceId")
set @cid = AttributeValue("CustomerId")

if empty(@cid) then
  set @cid = "0"
endif

set @js = now()

UpsertDE("Account Updates", 1, "EventInstanceId", @eid , "CustomerID", @cid, "Journey Status", @js) 

]%%

It's a good practice to code your email assuming that any of the incoming values can be null. The AttributeValue() function will return an empty string if the personalization string is undefined.

So as I posted this question, an email came through from Salesforce support thanks to auto case opening we have when any of our triggered sends are paused due to an error and the error gave me the information I needed.

In case anyone else comes across this thread and has this problem, the issue occurred becase we implemented a feature to auto-append utm tagging to emails for google analytic tracking. We set it up such that if the utm tagging areas are left blank in the email's properties pane that the utm_campaign would default to the email's name and the utm_source would default to the email's sendable data extension.

When sending from a Sales Cloud sourced journey Data Extension, the DE name is VERY long and cumbersome- when this defaulted, it caused a character count error and the email could not send.

This did not show up in the Send Preview becase the auto append utm tagging feature we implemented does not actually 'work' until the email is actually sent.