This is revisited version of the article, that contains all the data gathered regarding this issue. It explains what 'limb damage bug', 'cascade bug', or 'magic damage' is.
It seems that certain effects are able to 'overload' the damage transfer between the client and the server. The effect is most likely to occur the higher the 'computational complexity' of the damage dealt. It's unlikely that each single hit we deal is being sent to server on their own, most likely they are getting packaged into packets (so, i.e. a second long series of JE gatling plasma is all sent as single damage packet). The more calculations are put into one damage packet, the higher the chance for effect to occur.
The more pellets given gun releases on shot, the more complex the damage calculation (think Tesla), the faster the firerate, the greater the lag in client-server communication - the more powerful the effect.
Two-shot doubles the computational complexity of single-projectile guns. The most OP and broken weapon in the game is Minigun with Two-shot and one of broken major effects.
This piece of information has emerged in discussion happening on Dataminers discord 'FO76 Datamining'. Eckserah, the person thanks to which we all have our nuke codes, has looked into what is happening, and is now attributting the issue to this record and the change that was done to fix the Furious and it's tendency not to work at all.