@Philip O'Rourke Thanks for reaching out.
In polling trigger where you specify the time when you want to check if there are any new items available. If there are multiple items available and you have specified, (on) the Split on condition then your individual items will be executed in different instances of the workflow.
In your case the trigger is not a polling trigger so ideally all the new email would be running in the different instances of the workflow.
The other option concurrency control you define maximum instances of your workflow that could run at the same time. If you have disabled it, then by default multiple instances would be running processing different emails as per your trigger. If you enable it and set the Degree of parallelism to 1 then it means only one instance of your workflow would be running and at a time one email would process from your workflow. Once it is completed and if there are any other emails that are in queue will be processed one by one.
How can we populate array in logic app with the value of attachments if set splitter off? It is for the emails and not for the attachment.
Is there somewhere that can set polling interval to determine when checks to see if email flagged? Occassionally see trigger firing at 9.45 p.m. for some reason even though no email sent then as if some delayed run? Only for the polling trigger you can find the configuration to check for items after a particular time. Sometime there could be delay of few min.
Notice in New Designer View not even a splitter option to disable. Split on would not be valid as it not the polling trigger.
Hope the above clears your concerns and let me know if you have any queries or concerns.