Split on customer TYPE (not customer ID) is what I was recommending. Based on your data set seems you only want "Full Time"

Have you tried a split on customer type then a dedup on customer id? in the dedup you can use the advanced tab to keep the oldest or newest based on the date.

Delivery-> Delivery Scheduling -> Contact Date = is the date the email was sent to the recipient.broadLogRcp -> Event Date = is the date of an Open or a Click. broadLogRcp -> Url - > Type = Lets you pick between Opens or Clicks If you use DateOnly(@eventDate) equal to DateOnly(DaysAgo(3)), this is o...

Have you double checked you have accounts created for the past 30 days? Can you see that in the data schema of the table? Unless someone created that specific data field for your instance you may need to use a different field. The date a recipient profile is created is called creation date. Event da...

Seems like an MTA issue. Submit a ticket to support to verify that the MTA's are processing requests and sending them through the SMTP.

Are any delivery templates working? If everything is stuck in pending I would look at your typology rules in properties. Its possible its stuck in pending because it can't find it's way out through the MTA. 

The DCE is somewhat limited. If you are building an email, then you would want to make sure you have enriched all your data in the workflow from other tables. Then can you use <%= targetData.columnName %> to pull in data from the workflow. If you are building a web page you need to run a query as yo...

Have you ruled out email bot traffic? Does it happen on other recipients, email domains ect.?

External Signals are very powerful. Used in both internal (workflow to workflow) or external (HTTPs API call to ACC trigger a workflow or process.).Check out this link for more examples.https://blog.floriancourgey.com/2018/07/call-another-workflow-in-adobe-campaign

It should keep each iteration. But it is not recommended as it can cause the workflow to get bogged down. The use case is pretty strange. If you just got an update why would it be held for another 2 hours?  I would break out what you have into two different workflows. One to run the query every 30 m...