I have a strange issue that I cannot quite resolve.

We're running Umbraco 8.13 with uSync complete edition 8.9.6. It works perfectly on my local development environment, but on our Testing and Acceptance environment something doesn't work.

I create a sync pack from the testing environment and attempt to import it on our acceptance environment. In the differences it shows several changes that it's going to make. I accept the changes and start the import, it finishes instantly and says: "no changes". When I look, I indeed see that nothing has been changed.

I don't know why though. First it says that it will make changes, but then it doesn't make the changes. If I import the sync-pack on my local development environment, it works as expected and changes are applied, so it appears to be related to our hosting environment

Here's what I've checked:

• The hosting environment has a strict firewall. If it doesn't like any request, it cuts it short, returns 200 with a message in the payload that says that the request is not allowed. Looking in my devconsole, I see no such responses from the server.
• The hosting environment has no write access to the usync folder on the filesystem. I recreated this on my local development environment, but could still import the sync-pack without a problem.
• We've attempted to update uSync to the latest version. For some reason uSync publisher stops working on specifically our acceptance environment and says it can not connect to the other environments or to itself, whereas it still works on testing for some reason, so we had to roll-back the update.

Does anyone have any ideas why this happens and most importantly: how to solve this?