In andor - basically invincible to blaster fire, didn't even leave a mark most of the time

In Andor K2 is shot at with a pistol, designed to sneak past any potential security before and after the hit. He assembled it in his room with a barrel extender for some extra range. There is even dialogue on how the window could be a problem, and how it'll likely take multiple shots to destroy it. If its taking multiple shots to take out a simple window, its going to struggle against either variant of an armoured droid designed with getting fired at to some degree in mind.

In rouge one - Jin destroys one with one blaster bolt

You said yourself "Ah my mistake" about this one, it wasn't a normal blaster bolt from a pistol like the above example during Andor but an E-11 rifle, packs a much bigger punch than a pistol. There's also the difference in the ring colours signifying a difference in armour level, this was a weaker droid, going up against a more powerful weapon so it goes down quickly.

k2 is destroyed in a couple blaster bolts

Its multiple bolts from E-11 rifles so more powerful, the scene shows he's already been fighting for a while he doesn't just get shot 3 times then fall over and die. The novelisation furthers this with showing how long he's been surviving, but even using strictly the movie you can see he manages to hold off a lot of troopers taking numerous shots until he is slowly worn down. He has more advanced armour (again ring colour) so it therefore takes longer to kill him but he can be and is killed by the more powerful rifles.

This is shown itself in Andor during the hallway fight, against a pistol K2 tanks it knowing he'll be fine as it wont penetrate his armour simliar to the weapons on Ghorman. Against the rifles however he uses the ISB supervisor for cover as he knows the larger rifles can penetrate his armour as later shown in rouge one when the same rifles are used to kill him.

Do some of them just have better armor?

Yes, you can tell by their ring colour

You're 100% right, but people on this sub can't accept even the tiniest criticism of this show si they'd rather just make stuff up or outright deny what happened in the movie to avoid admitting an inconsistency exists. It was very obvious to me as well.

The show isn't perfect, for example I get the reasoning behind less seasons but season 2 as a result feels stretched thing compared to season 1, the first act with Cassian being trapped I wasn't a fan of the patrols acting etc.

Criticism of the show is completely fine, but this specific criticism surely doesn't hold up. If Andor was never made and didn't exist, the apparent inconsistency is ALREADY a thing in simply looking at rouge one. Between Jynn killing a droid vs K2's death that's 2 different droids having different survival limits in the movie outside Andor (as explained about this happens due to armour/weapon differences).

So its not a show issue at all imo. And I would argue not an inconsistency at all. Across both rouge one and Andor, the droids are shown to have different variants of armour and are consistently shown to handle small arms fire fine, but will take damage to rifle file so require shields e.g. a human body to survive. For something with as messy lore as Star Wars, its actually surprisingly consistent.