We have T58191, T59333, T60733 open already.
Without having your .blend file it is kinda hard to decide which report to merge into, my guess is we are dealing with ngons here? (then it would be one of the later...)

This is just a clear warning/error that that modifier has severe limitations in sculptmode.
Spitting this to the console was added in rB552b2287db86.
I personally dont mind having this in the console as well and would lean towards not calling this a bug...

Steps to reproduce the file:

1. Delete everything from default scene
2. Add Cylinder
3. Add Cube (Will not work with default cube.)
4. Scale Cube by 3
5. Scale Cube by 0.5 along Z axis
6. (optional, but better visibility) Set Cube 'Viewport Display' to 'Display As: Wire'
7. Add Boolean modifier to Cylinder with 'Target: Cube'
8. Move Cube along Z axis (somewhere between -0.5m and 1.5m)

Note: Order of steps does not really matter, but the scaling dimensions are somehow crucial.

I still can't make this happen. Can someone who can make this happen please upload a simple .blend with a cylinder and cube with boolean modifier set to difference where the result of the boolean is the union rather than the difference?

For this case, CustomData_get_layer_name(cd_ldata, CD_MLOOPUV, i) apparently cannot get a layer_name...
@Clément Foucault (fclem) might be interested?

More than a week without reply or activity. Due to the policy of the tracker archiving for until required info/data are provided.

More than a week without reply or activity. Due to the policy of the tracker archiving for until required info/data are provided.

We do not handle user support on this tracker, only bug reports. User forums like blenderartists.org or blender.stackexchange.com and our devtalk should be used for that matter.

These shortcuts were intentionally changed to be used for mode switching with expand selection.

This is probably a mistake in rB87629b2a7443

Can confirm, checking...

Thank you, Demeter (hope I'm not confusing your name with your family name :) ) . That bug, or what it is, looks pretty old (reproducible in every Blender version I tried - down to 2.61) but only in 2.80 it somehow gained prominence. I consider it critical cause you don't want your character flashing with random mesh explosions during animation and not using b-bones at all also not looks like a good thing. But with 200-300 open unsorted bug reports and few dozens new a day you, developers, sure have your hands full.

Confirmed, 2.79 has the same issues...

@Philipp Oeser (lichtwerk) you're right, this case should work.

Hm, thing is, even if the deforming curve is 2d only as well, then triangulation fails as well... see [Fill deformed is ON here]

Can confirm triangulation is not great here, maybe @Campbell Barton (campbellbarton) has an idea?

Please include a blend file which crashes when the modifier is added.

can you upgrade to latest drivers (431.xx) from Nvidia support site, now you use a quite old drivers and check newly for you problem

Can confirm for any mesh with a modifer (since rBAe5c3ae311 the mesh name cannot be changed anymore it seems...)
Will check in a bit...

I can reproduce this. The "detail" of the glitchiness depends on how many bbone segments there are, but the bbone segments themselves are not moving in any unexpected way, like OP said, only the mesh. So I'm guessing the problem is where the double quaternion armature deformation from bbone segments is being applied to the mesh.