No need to look at logsYou shouldn't have lost root, a simple oversight of selecting the stock boot instead of the patched boot after creating a patch and before hitting the flash button could cause that.
You'd think you wouldn't make a silly mistake like that, well I've got news for you, I did that mistake and lost root, and wondered if I had introduced a regression in the latest release, only checking the logs exposed my shortcomings.
I can take a look at you logs if you want.
Another possibility is that the last step in flashing is actually flashing the patch, if anything goes wrong during that, the phone will remain in stock state, not that something should go wrong, but anything is a possibility.
I am sure I did select the patched boot img as there were 2 there to choose from.
On March update if it happens again I will post logs