Animating a boolean operation gives inconsequent results I'm trying to make a water level rise in a tube, but both in the viewport as in the final render, boolean action provides inconsistencies. I'm using Blender 2.83 for this.
Most of the times the boolean (an animated box using difference as operation) works as expected but some frames just produce a flat face instead of a volume. (3rd image)

I'm actually using 2 booleans on the water, one to cut the water in half vertically and a second one (animated) to rise the water level, but applying the first one doesn't make a difference.
I believe my boolean objects are big enough.
Here's a screenshot of my setup:

It doesn't make any difference if I make the animated boolean an intersecting one either.
Does anyone have an idea how to fix this?
Here's the project file(s) just in case:
BoolTest01.blend (Boolean as difference)
BoolTest02.blend (Boolean as intersect
I only looked at your BoolTest01.blend file.
First I applied the the Modifier on the &quot;Water&quot; object that had the &quot;B_Box halving&quot; as a target object. Then I applied the rotation of the &quot;Water&quot; object: 3D viewport &gt; Object &gt; Apply &gt; Rotation. After that the glitching seemed to have disappeared.
Hope that (also) works for you.
EDIT:
I've seen some strange things happening in your third file. Among others, on opening the file the &quot;Water&quot; and the &quot;Box halving&quot; behaving as one object when trying to select the Water. And getting a kind of &quot;can't assign value&quot; message (don't remember it exactly and didn't record it) when trying to apply a Boolean modifier at some point.
Also tried a bunch of things to fix your problem. Making the cylinder have an all quads topology and reapplying the Boolean modifiers in various ways.
I was almost out of ideas, but i found another fix that works for me. It is not ideal, but it might be adequate.
I believe the perfect aligning of the side of the &quot;Box halving&quot; and the height edges exactly in the middle of the &quot;Water&quot; cylinder might be responsible for confusing the boolean operation.
So i moved the center of the cylinder slightly to the side (1 mm according to the MeasureIt Tools; hardly noticeable) and that made the glitching disappear.

Again, i hope that (also) works for you