I am trying to refresh the source schema in my MYSQL source (3.5.0) on Airbyte 0.63.9 but it is giving me a "An unknown error occurred. (HTTP 504)" error. Tried for several weeks now, didn't work on our previous Airbyte version either. Can't find anything in the logs.

I'm sorry to hear that you're experiencing issues with refreshing the source schema in MySQL on Airbyte. Based on the knowledge sources provided, it seems like you might be encountering a timeout issue. This is suggested by a similar problem discussed in a [Github discussion](https://github.com/airbytehq/airbyte/discussions/40738) where a user was getting a "HTTP 504" error when setting up a new connection. Unfortunately, the knowledge sources do not provide a direct solution to this problem. However, they suggest that the issue might be related to a timeout limit, possibly with nginx. The user in the Github discussion tried to check the status of nginx in the docker container and found it to be inactive, but it's not clear if this was the root cause of the problem. In another [Github issue](https://github.com/airbytehq/airbyte/issues/29712), a user encountered a similar error when the process of fetching database schemas took more than 1 minute. This suggests that increasing the timeout limit might help, but the knowledge sources do not provide specific instructions on how to do this. Given this information, I would recommend reaching out to the Airbyte community or support for further assistance. They might be able to provide more specific guidance based on your particular setup and the exact error message you're seeing.