So - silly question.... but if there are two log items approved and another new item added, if the user clicks an "approve" button not associated with individual items, how do they know what they have approved? Is it just generally accepted it would apply to all that are not currently approved? Or if two are approved and one is submitted, and I now click a "decline" button not associated with individual items, how would I know that I'm only applying that action to the submitted item? What if my intent is to now decline all the items? How would I do that?
However, to answer your actual question - if the Log this Activity button was outside of the section, I'd use a qRules command to just set the rows with a blank status like this:
SetValue /xpath=/my:myFields/my:ActivityLog/my:group11[my:ALStatus = ""]/my:ALStatus /value=Submitted
I'd probably set the other fields first, so I could leverage the blank status as an indicator of what to set:
concat("SetValue /xpath=/my:myFields/my:ActivityLog/my:group11[my:ALStatus = '']/my:ALSubmitDate /value=", today())
Then, it doesn't matter if all the items resubmit to the list, because the existing items won't have been changed.