Hey @jshubin,
This is known defect that is under review.
As a workaround I've had some success using blocks when selecting the create equipment function and containing a base block from an existing support:
Note this is a lengthy process and a bit strange but does yield a decent result.
I started with an exploded structural beam and a pipe.

Insert a simple support:

Set the width or thickness to 0"

Rename the block to something known - a support number or name like so:

Modify the renamed block to add our beam.

Create a new piece of equipment and select the option for block based:

Insert this support inline:

Verify the support is valid and connected and then edit the block in block editor (to remove the cylinder)

Subtract the cylinder from the beam - quick tip - when using subtract select the beam first and then the cylinder.

Save and close block editor and see below:

Assign and SKEY and run an ISO:

This worked for me whenever i tired it - VERY important to start with a dynamic support - i do not know why but it works when you do so. It did not work to select a purely created ACAD block that did not come from a support, hence the extra steps using the simple support.
Ryan Bales
Fusion 360 Product Support