Nothing was wrong with rev3 - it just was never produced - the rev3 files were just like rev2 (of which we made 30k units) but had a few adjustments for better production. At the point those changes were made we released the files for the first time publicly, so we publicly released the rev3 files.
Before we produced the next batch of 10k units we made an additional change - we lengthened the USB connector - and so we named that rev4. Nothing was wrong with the rev3 files, but since they were publicly released and never produced by us it became an easy way to know if a device is a "clone."
The reason most of the clones don't work or have issues is because they use the wrong parts all together, parts that are bad/second hand, or parts that are improper substitutes for the USB to work. Many also lack the bootloader or don't have the fuses set properly.