Here are some suggestions:
- Do not disable ANY failsafes, they are there for a reason.
- Check that you are not using hardware that should be avoided
- Make sure to follow these hardware best practices
- Enable RC, mount the GPS and configure the vehicle correctly
- Tune the PIDs
- Once that is done and the drone operates reliably, remove the RC and the GPS and try again.
I edited the title of your post to better reflect the content