I've now done a second board with Zealios (65g this time, rather than the 67g of the first) and again have 0 problem keys. To be honest, the soldering is even worse this time - I somehow got worse at it, and I'd be ashamed if anyone else saw the bottom of this PCB.* It makes me really doubt that soldering is at issue unless people are jamming the iron all the way down under the pad and somehow touching the switch bottom, or at putting on so much solder that it's dripping through the hole and melting the area around the pin. Are the chattering keys showing up for people with PCB builds, or handwire? I could see a handwire build going a bit more awry heat-wise, but I've never done one so not sure.
Impressions - the 65g feel much closer to ergo clears than the 67g do. It's amazing that 2g of resistance can make this much difference. I think I overall prefer the 67g - they feel much snappier, there's a really nice bounceback after the keypress which is missing to some small degree in the 65g (though it's still present, just a bit less). I prefer heavier switches in general though so YMMV. The 67g are also a more "unique" switch to me - again, the 65g are pretty close to ergos to me, while the 67g don't feel like any other switch I've tried (including Topre, though I understand the comparison now). Hopefully the 62g tactile come back with round 2 so I can be financially irresponsible enough to build a 3rd Zealios board!
* A fully transparent case was a bad choice in this regard, as cool as it looks otherwise.