My current Beta 3 config, migrated from 20.0.3, has just a single C/C++ language alias defined. I have many (some by default, others that I created) in 20.0.3. I'm running on Windows 7 x64 and attempted to migrate again from 20.0.3 and on first startup of 21, the C/C++ aliases again had just a single alias (tag) defined.