Often, when I try to debug a package in RAD Studio (the host) by debugging the package with a new instance of RAD Studio (the debuggee), the debuggee would hang some of the time while loading its packages.

It turns out that the hang was caused by a feature introduced in Windows 10, called Parallel DLL loading.
Parallel DLL loading speeds up the loading of DLL dependencies by spawning multiple threads to load DLLs.

To enable Parallel DLL loading:

reg delete "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\bds.exe" /v MaxLoaderThreads /f
reg delete "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\bds.exe" /v MaxLoaderThreads /f /reg:32

To disable Parallel DLL loading:

reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\bds.exe" /v MaxLoaderThreads /t REG_DWORD /d 1 /f
reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\bds.exe" /v MaxLoaderThreads /t REG_DWORD /d 1 /f /reg:32

For me, it turns out that parallel DLL loading is the cause of many exceptions and hangs that I've seen with RAD Studio. Disabling parallel DLL loading fixes it.