I have uninstalled both compilers and re-installed.
Is there only one "unified" compiler now? I notice that the name of the compiler in the beta downloads page says "Download PureBasic 5.72 Beta 1 for Windows (32-bit and 64-bit)."
[UPDATE]: I noticed that I can add the other architecture compiler under Preferences/Compiler Options. As far as I can recall, this used to happen automatically. I may be delirious though.

Thanks!