It typically means the service providing the graph data is experiencing an outage, but it could also indicate an unstable internet connection, a problem with internet installed driver, or an issue with the app you are using (Trezor Suite in this case). Usually, if the problem persists, it is likely a temporary issue with the service hosting the graph data. You may need to wait and try again later, as suggested by the error message itself.
Honestly speacking, i have never thought enabled VPN would cause the same error message. Probably a server error or if Thor is installed.
Anyway you should get off Trezor as it's not the best solution nowadays
Why you suggest this? Trezor is one of the the most trusted wallets in the market nowadays. Please provide more details about the observation you provided and it would be more accurate if you can suggest alternatives.