I'm working with Gilderoot on this and wanted to add some more detail that we have uncovered today.
today we have made a copy of portal 3 and used it to create a new dnn site (portal4) we have them done a product export from portal 3 and imported it to portal 4.

we once again saw this issue where in the back office we were seeing products from portal 4 in portal 3, we could tell they were differnt as some of the product images were broken in portal 4 and also if we tried to edit the products in portal 3 we would be redirected to portal 4.

I was working on the theory that we could only see portal 4 products in portal 3 because I was logged in as a super user and have the ability to see all sites and stores with the same login. So I created an admin user, same level we would give a store owner and was doing my worked logged in with that them on portal 3, I had a couple products in my cart and went to go to checkout and the store redirected me to portal 4 and told me my cart was empty and i was of course logged out.

Further testing revealed I could duplicate this error when logged out of any user account. eg as a customer to one website I was being redirected to another website when clicking on products.

a couple of things to note
[list=1][*]all these sites are on the same instance
[*]portal 1 and 2 are live on their own separate domains.
[*]portal 3 and 4 are not live and are on subdomains structered like this abc.mydomain.com and xyz.mydomain.com[/list]

I have screen rerecorded most of these errors and would be happy to share via direct message/email if anyone wants to take a look.

Hoping someone can help us here as we are desperately trying to find ways for our clients to be able to keep operating over this challenging time for them.

We have done some more testing and have a little more info to add:

[list][*]we can reliably trigger this event by completing a product import as a super user
[*]we can reliably trigger this event when completing an import as a Administrator user
[*]we can resolve the issue only by recycling the app pool after each import.
[*]clearing cache does not seem to resolve the issue[/list]

Whilst this is manageable at the moment we are hoping to hand the store over to the clients soon and there is a very real risk that they will perform an import and therefore break not only their site but our clients sites on the same DNN instance.

[b]Does no one want to jump in here with some ideas?[/b]

From what i can see a product import on an instance will cause all other HCC stores to drop their setting for a moment. this is causing major concern when a users is completing the order in checkout just as an import is beingcompleted on another portal and no shipping costs gets applied to that order.

Honestly, this will require some troubleshooting. I'm unable to offer any meaningful feedback until I can find some time to do that.