When you say all your other trigger nodes do you just mean other Hubspot Trigger nodes? If you check the webhooks registered in Hubspot does it already exist and maybe just hasn’t been cleared properly by the node?
Do your custom trigger nodes show the same error message? My worry here is that you mentioned “all other triggers” which could be a larger problem.
I take it you have tried making a new workflow as well? I have tested here on my n8n instance and I am able to create a trigger for Hubspot with no issues so we will need to start looking at more details to try and work out what is happening.
Other bits that would be useful would have been in the template for new posts.