While I'm not seeing any reported issues recently regarding the internal error response on the List Events endpoint, in order for us to troubleshoot further, could you share with me the following:
1. The portal ID in question
2. What's the exact internal error that you received
3. Additionally, I'd like to add that it is not uncommon to see a certain number of 500 errors. Typically, retrying your requests should almost instantly fix the issue. Have your team tried retrying the requests?