I've come across an issue while using various attribution models and different scopes with my Marketing Channels.
The thing I can't fully grasp is the "none" bucket when using a "visit" scope because the "none" bucket does not appear in my normal Marketing Channels report (using the same metric related to application submits).
"none" value shows up only for First touch and Last touch so my theory here is that on visit scope, no First touch nor Last touch could be identified. In other words, these channels were identified beyond the visit scope. I would greatly appreciate any ideas on this.
Nonetheless, when using the visitor lookback the "none" bucket does not appear which leads me to the conclusion that might support my theory about the First touch and Last touch not existing within the visit lookback window but they must naturally appear within the visitor lookback window.
When applying any Attribution model to your metrics, the data points that are used to generate the metric numbers come from what was captured ONLY during the date range you specify in your report.
If your report's date range went from May 1 to May 31, for example, any data that were captured before that point (e.g. on April 25) will not be accessed to generate the metric and breakdowns, even if the data values were meant to be persistent beyond the point they were captured. eVars and Marketing Channels are meant to persist when using the "out-of-the-box" metrics (i.e. when NO attribution models are applied), but this persistence is completely ignored when you apply an attribution model.
You most likely have instructed the "Direct" channel (and most likely "Internal" as well) to not overwrite other marketing channels when visitors come back to the site - that's perfectly normal and considered a best practice. However, with such a setup, you will very likely have some visits during your report's date range where no marketing channels were recorded. Direct might have been recorded in such visits but the marketing channel setup specifies that Direct shouldn't be recorded if visits previous to the current one recorded a different channel. For these specific visits where no marketing channels were recorded, the Attribution Model (applied at the visit level) will have no channel to work with, and hence you get the "None" bucket.
Hopefully this makes sense, feel free to reply if you need clarification.