For the first time in a while I encountered a couple of files with extension .__a, .__b, .__c, and so on. I’m familiar with multi-part rars, but when I tried to open the .__a with RAR Expander I was out of luck.

On the Mac, one solution is to download the program Split & Concat. Then, and this is important, rename the files from .__a, .__b to .001, .002 and so on. Open Split & Concat and choose “Concat”. Select the first file (ending in .001) and Split&Concat will extract the file. If you feel like it, donate to the developer. It’s a good program.