I have just sent a load of troops to liberate a friend and when they got there, they disappeared. No report and the units did not return.
Have now got units back but still no report.
Since the latest upgrade there have been multiple errors, making the game unstable.
This sounds like your friend got liberated before your units arrived to him, making them regular reinforcements (and, thus, exposed to any attack). You likely got them back because he sent them back to you.
Missing reports usually appear after a reload. This bug is nothing new. As a matter of fact, it has (had?) its third birthday one of these days. Sadly, I forgot the exact date when it was introduced, so we cannot celebrate precisely. In my naivety, I didn't expect a "missing reports" bug in a "strategy" game to go unfixed for 3 years. Silly me. 
