Well, it seems that either UV Layout SOP or Match Current Definition has a beef with me. I'm not going to speculate which one of the two is the culprit, so I'm just going to describe the problem that I'm experiencing in the current production build (20.5.278).

The video depicts my antics with UV Layout SOP nested in an HDA. Newly created UV Layout operator works fine, but once the asset is saved and its definition is matched, UV Layout SOP breaks. What is weird is that a copied instance of that very same operator repiped to the flow works just fine. Until of course I save and match the definition of the asset. Also, the malfunctioning UV Layout SOP "fixes itself" after the scene containing the asset is reloaded. Of course until I save the definition...

I'm sorry, but even though I consider features implemented in 20.5 to be of huge significance (Copernicus, MPM), I feel that I'm spending most of my time fighting bugs and restarting the program.

And please, get the external dependencies off from the new shader ball. :/

Looks like a bug in the UV Layout SOP. Can you submit a bug report?
Also, it looks like there is a warning flag on the UV Layout SOP which might give some clues about the buggy behavior.

Will do, within the next few days. Thanks, Justin.
The only thing that the flag tells is that Some islands failed to pack. It's visible on the video, on the docked Node Info pane.

I have the exact same issue.

The UV layout SOP works if I create a new one, but then it'll break again. I also get the "Some islands failed to pack" warning - resulting in no layout happening whatsoever. I've never had this issue before H20.5.

ajz3d, have you been able to share your file with SideFX?

Sadly I can't share min, but it looks like you've got just a cylinder, so maybe you can?

If you haven't also reported the bug, this is my SideFX Support Ticket: #156552

I reported this bug yesterday. Its ticket number is #156601.

To sum up:
Contrary to my original belief, the bug is not caused by "Match current definition" in any way, but by "Stack Identical Islands" of the UV Layout SOP itself.

The bug can be reproduced with just a Box, UV Unwrap and UV Layout SOPs piped together in this order. Enable "Stack Identical Islands" and the UV Layout breaks and becomes beyond repair. And what I mean by this is that the operator will no longer react to changes of its parameters. Unchecking this flag doesn't fix it. Duplicates of the broken node work, until I enable "Stack Identical Islands" (at this point they'll break in the same way). It's reproducible 100% of the time.

The only remedy is to delete and create a new instance of the UV Layout SOP.

Both 278 and 332 production builds are affected. I also tried running Houdini with default user preferences, to see if perhaps there's some interference coming from external packages, but UV Layout still breaks.

I'm on GNU/Linux BTW.