Systems can be finicky in proportion to their refinement. Here are a few thoughts out loud....
I don't know anything about the Atmos, but if the cartridge is that new, I'd get it past at least 60 hours before worrying too much. Cartridges can act inconsistently from day to day during their break-in period. E-mail Mehran (?) and ask him what to expect for break-in.
If it is at a "particular place in the lp" - could the record have a small warp or bubble in that part of the groove?
Has there been any significant temperature or humidity change during the day to evening period where it happenened then didn't then did? I'm not sure if temperature/humidity can affect your cartridges compliance, but I suppose it is possible.
I doubt that compliance is the issue. The Triplanar and ZYX should be a good match. But since your symptoms sound like a similar experience I had , I'll relay it. Several years back I had mistracking issues with a Grado Sonata on a Premier MMT tonearm. Always on the first band of a side closer to the lead-in. I'd get mistracking on most any Telarc I played. It was an issue of stylus/cantilever compliance - Grado's were undamped (may still be for all I know) - which got sorted out as a cartridge/tonearm matching issue. When its not quite right, resonance can occur that causes what you describe as a 'flutter'. Increasing the effective mass of the tonearm or introducing some form of dampening both helped my situation somewhat, but not completely. You can change the effective mas by adding a gram of modeling clay to the headshell (and adjusting VTF) to see where that takes things. Dampening can be added by using some silicone (?) in the arm's dampening trough. You might observe the stylus/cantilever closely when the problem occurs to see if you notice any unusual 'wiggling' motion before and after experiments you may try. Again - unlikely that its compliance, but those are my thoughts.
I don't know anything about the Atmos, but if the cartridge is that new, I'd get it past at least 60 hours before worrying too much. Cartridges can act inconsistently from day to day during their break-in period. E-mail Mehran (?) and ask him what to expect for break-in.
If it is at a "particular place in the lp" - could the record have a small warp or bubble in that part of the groove?
Has there been any significant temperature or humidity change during the day to evening period where it happenened then didn't then did? I'm not sure if temperature/humidity can affect your cartridges compliance, but I suppose it is possible.
I doubt that compliance is the issue. The Triplanar and ZYX should be a good match. But since your symptoms sound like a similar experience I had , I'll relay it. Several years back I had mistracking issues with a Grado Sonata on a Premier MMT tonearm. Always on the first band of a side closer to the lead-in. I'd get mistracking on most any Telarc I played. It was an issue of stylus/cantilever compliance - Grado's were undamped (may still be for all I know) - which got sorted out as a cartridge/tonearm matching issue. When its not quite right, resonance can occur that causes what you describe as a 'flutter'. Increasing the effective mass of the tonearm or introducing some form of dampening both helped my situation somewhat, but not completely. You can change the effective mas by adding a gram of modeling clay to the headshell (and adjusting VTF) to see where that takes things. Dampening can be added by using some silicone (?) in the arm's dampening trough. You might observe the stylus/cantilever closely when the problem occurs to see if you notice any unusual 'wiggling' motion before and after experiments you may try. Again - unlikely that its compliance, but those are my thoughts.