Be aware that if you get Magma compile errors regarding certain MIDI notes, it will report a location as #.#.### (like 5.2.393 say)
But when you go to look in Reaper at your notes (or text events), and if you bring up the Properties window, it will display like this: #.#.## (like 5.2.39) (see attachment)
This caused me no end of frustration at 1am when I was trying to compile and I didn't figure out what was happening until today.
I would keep moving notes around trying to find the one it was referring to in the Magma error, and I could never find it. I didn't think to look in the Midi Event list, where you do get the full three digit display.
I found this problem in the Mac and Windows versions of Reaper 3.12.