From time to time my macOS applications enter the twilight zone wherein adding, for example, a memo to a form compiles but the application dies when run with "Class TMemo not found" and sure enough, when I check, I find that "Memo1: TMemo; " is missing from the source code.
Unfortunately I have not previously been able to track down how/when this behaviour is triggered which means I have not been able to provide a minimal demo project with the issue... until now because this project is small enough to upload and was only used to test various macOS features
See attached. Compile and run -> "Class TMemo not found". Delete the memo and add it again. Same result.
You will obviously need macOS.