Alternating layers with zero seconds long layer  

Alternating layers with zero seconds long layer

Hi, 

I'm guessing that this has likely been addressed before, but when I try to search for it, the results I get are about poor layer quality. 

Anyhow, I've been happily printing with PrusaSlicer, and have got my performance settings dialed in nicely. 

I am printing on a RepRap based printer with a Duet3D card (RPi daughtercard) on a Core XY machine called a HevORT. I've been printing with it for more than 2 years, previously using Simplify3D, and switched over to PrusaSlicer in the past couple of months. 

When, like many of us do, watching my printer, I can see the layer chart on occasion, where it for a period of time is going between what looks like a normal print time (many seconds) for a layer, to a layer that has a print time of zero (0) seconds. And often back and forth for a number of layers. So, normal layer time, 0 layer time, normal layer time, 0 layer time, etc. Usually on layers with small print times. 

I have to assume that  this is normal, as the prints are coming out fine. 

However, for these prints, I did NOT select the Variable layer height function. Or at least I don't think I do. I thought you have to select the icon for variable layer height from the top and then do the export. 

But when I look at the layer report, which shows time and layer height, it is showing different layer heights. 

Is there someplace else I'm missing that allows for this? 

Am I just clueless?

Any help would be appreciated. 

Thanks

Michael