I think the coding of the background shader or environment texture must have changed somehow, because adding new ones seem to be back working as expected....although I did think that the behaviour of the slider used to update the render as you moved, now it seems to only update the render on mouse release which takes away the interactivity somewhat (which is important when tweaking lighting).

Might want to add a bit of code to upgrade the old node to the new node to avoid any more bug reports?

2.8 was very fast to update modifications to the hdri rotation, strength etc (the same as 2.81 is now that I deleted and replaced the environment texture node and the background shader). I was mistaken regarding 2.81 not initiating the update until the mouse button is released though, it updates when mouse movement has stopped for a second or two whilst the mouse button is still depressed.

Just to clarify, 2.81 and 2.8 both began the update process at the same time, but 2.81 was taking around 10 seconds to restart viewport rendering, whereas 2.8 restarted the viewport render in under a second.

Not an issue now I deleted and replaced the nodes, so presumably the code for one of those two nodes has changed between versions.

In T71519#810297, @Brecht Van Lommel (brecht) wrote:

It's because background multiple importance sampling is now enabled by default, which requires a rebuild when rotating.

We would like to optimize this in the future, but it's not a bug.

why would recreating the node resolve the issue?

I'm not sure. But the bug report is missing the actual .blend / image file and steps to reproduce the bug, since only steps to create new nodes are provided and those apparently work ok.

So, we must have that information first to confirm that it's indeed a different issue than just multiple importance sample updating.

ah ok, I couldnt share the file as it's under NDA,. If you want to replicate, you could create a scene in 2.8 which has a hdri, and then open it the latest daily build. It's definitely not caused by multiple importance sampling now being the default, otherwise new nodes would have had the same issue. I'll leave it with you.

Have you verified that creating a mapping + environment texture node in 2.80 and then loading it in 2.81 actually reproduces the problem? It didn't for me.

We don't require the original file in bug reports, just any .blend file and exact steps to reproduce the problem. Otherwise we waste time guessing what might be the problem.

The original file may have been created in one of the previous daily builds somewhere between 2.8 and yesterdays daily 2.81 build, I'm not sure which. When I've finished these few projects I'll have a dig around to try and find another file which has the same issue, or hopefully before then someone else will experience the same problem with a file they can share.

Awesome job to everyone over there by the way, I'd marry this program if it was legal :)