This is a very simple Houdini node setup but caused a file to become corrupted and crash Houdini when opened in some instances that I can't replicate 100%.
The simple version of the entire node setup is just:
geo / matnet / arnold_materialbuilder / standard_surface connected to OUT_material
Saving this Houdini file, closing Houdini, reopening the file shows the standard_surface node has completely disappeared, not only from the network editor but from the entire node list as well. You can't place back the standard_surface node because it apparently doesn't exist anymore when you search for it in the tab menu. Creating a completely new file also shows that standard_surface still doesn't exist. I had to reinstall htoa to get it to show up again.
These shenanigans also extended to the fetch node as well somehow and maybe a few others, causing another one of my save files to be corrupted which I could no longer open. Luckily I have backups.
If it makes any difference, I also have Octane for Houdini installed which Arnold likes to overwrite HOUDINI_PATH and PATH in houdini.env when I install Arnold by the way.