The TLS community knew that there would be problems with the deployment of TLS 1.3 with version intolerance, because there always have been. That's why the version negotiation was changed and a mechanism called GREASE was invented to avoid just such problems. But it seems BlueCoat has shown us that there's no way to anticipate all the breakage introduced by stupid vendors.
The takeaway message is this: Avoid Bluecoat products at all costs. These companies are harming the Internet and its progress.