Just gonna leave this here for those that are less tech savvy like me heh heh heh.
I have tried playing Co-op a while ago, and there is definitely no levelling issue:
https://imgur.com/a/6E8OOTU
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As for this:
Let’s just say that when it comes to technical issues, the most difficult part about troubleshooting has nothing to do with solving the problem. It is identifying the problem that is really difficult because just a single typo can break a lot of stuff. But once we can identify the problem (i.e. replicate the issue consistently), fixing it is a piece of cake.