Small support issues / Print As Support affecting overhead skins

[shenanigans 0]

Before I get into the problem, let's tackle the "why" issue and introduce the part I'm trying to print.

To supplement the bowden tube connector on my Ender 3 I use a simple collet clamp. This completely eliminates tube movement during retractions, drastically improving performance with PETG and TPU. The original part is one of the first successful prints I ever made! Unfortunately during maintenance yesterday I snapped one of the petals off the business end. It's still functional but I thought I'd take the opportunity to update the design and print it up a bit nicer. On the old one I did the threads left-handed, too. Oops!

 

The old one was also sliced in Cura. Version something or other. I didn't know enough at the time to check the preview properly so I don't know for sure how the supports were set up then. But it came out ok anyhow! But now I'm on version 4.7.1 and I'm having some issues.

 

The first issue is that Cura is recognizing the area inside the bottom hole as being part of the model instead of part of the build plate. The support doesn't want to print at all until layer 6 and won't print a full circle until much further up. No support will be printed at all if Support Placement is set to Touching Build Plate. Yes I have tried lowering Minimum Support Area. Yes I have tried it with and without conical supports. No I am not triggering my Small Feature Settings. No turning off Adaptive Layers doesn't help. The supports only start to print properly if you sink the model into the build plate up to the point where the internal cavity gets wider.

So I thought, this seems like a job for Print As Support! What could possibly go wrong?

Looking good, right?

 

The threaded section, however, is hollow with a central spire of support material.

 

It looks like the Print As Support model is causing skin layers above itself to lose internal holes. It has no effect on layers that contain only walls and/or infill. And here's the freaky part - sometimes the skin layers STAY screwed up even if you move the models around or delete the Print As Support part. This doesn't seem to happen every time but when it does the part must be deleted and loaded in fresh - altering the model and reloading with F5 doesn't help.

 

So for the moment I'm a bit stuck. My next step is probably going to be trying to estimate which version of cura I printed the original part on and rolling back. Definitely open to other suggestions though...