8-Internal : default rule modified (first page of visit deleted)
Marketing channels run on every single hit. If they don't match one of the first 7 rules on every hit of the visit, they're basically guaranteed to get caught under internal as soon as they click on anything.
If your question is "how the referrer becomes an internal referrer during a visit", the first thing we will want to check is your Marketing Channel processing rules. Would you be able to take a screenshot of them and list them here?
"Override last touch channel" is checked in the marketing channel manager, because if the referrer is internal, we want to populate the channel "Internal".
The visitor ID does not seem to change during a visit.
I just don't understand how the referrer becomes an internal referrer during a visit.
I have read this document : Referrers : "The referrer, referrer type, and referring domain are set on the first hit of the visit, or during a visit when the referrer is external (for example, if a visitor leaves your site, uses a search engine, then returns to your site before the first visit expires). These values are set at the same time and persist across the visit."
If a visitor uses a search engine, the channel will be "natural search", but not "internal". What if he comes back by typing our URL ?
In the marketing channel manager, is 'override last touch channel' checked for internal?
Another thing you'll want to double check is to make sure that the visitor ID in your implementation is not changing on you mid-visit. You can use the Experience CLoud debugger to confirm variable values on your site.