Greetings wolffspider!
Thank you for reaching out to us.

In order for us to properly assess your issue, could you attempt to log in again, prompt the Fatal Error to happen again, then share your most recent log file with us, please?

You can find it by following:

Steam\steamapps\common\Conan Exiles\ConanSandbox\Saved\Logs

Feel free to reach out in private via direct message with the log if you prefer.

Thank you in advance.