As the title suggests, there appears to be a significant issue with the decompilation of Objective-C code.
In libraries extracted from the DSC, many entries in the __objc_stubs segment are simple branches to objc_msgSend. IDA assigns these functions a variadic signature, but the decompiler frequently overestimates the number of arguments passed at a call site. As a result, the decompiled output includes variables that do not actually exist. These variables are shown in red, and IDA also displays a warning at the top of the decompiler window.
I do not remember encountering this issue in the past, and I have not been able to determine exactly when it started.
Apple changed the way these stubs are organized in firmware version 27, which you addressed in Beta 2. However, the same issue also occurs with firmware version 26.