Which alien are you hitting? For the generic McAlien, no, it's not normal.
Actually, from a brief glance the only enemy that's even vaguely likely have such a resistance to being tased is a Reaper.
Any Alien, even Sectoids. Several times I had 3 soldiers around the Sectoid, each soldier attacking 5 times with the stunt rod, and no stunning.
The report is too vague to tell for sure. It could be that the soldier is not even hitting the target. It might not be easy to tell if you are not a veteran player. In contrast to vanilla, there are a couple of factors which might make it more difficult to hit the target compared to vanilla. Melee accuracy affects stun rod accuracy, and melee dodging feature increases the chance of missing to some degree. I suppose it's more likely that the soldier is missing than the enemy unit is resisting the attacks.
I mean, contrasting to vanilla where almost any alien would go down with one hit. Maybe the toughest (like Mutons I guess) would go down with 2 or 3 hits.
I thought about the (new compared to vanilla) 'melee accuracy'. It my be that. How can I know if a melee attack actually hit the target?
If it is that my soldiers are not even hitting the alien, Does it mean that I should only equip with stun rods the ¿strongest? soldiers and the ones with most melee accuracy? is that it?
Any tips for stunning aliens in FMP?
Thanks very much in advance.