May be a setting or this may be something that has been in 2015 and 2018 now for a while, I'm coming from 11.6.3 and 3.07 I think it was.
It seems alot of things don't AUTO UPDATE in IPR now. I have to press REDRAW or RELOAD. Ie...if I change the HDR image for an environment....sometimes lights and such don't update.
It could be related to the amount of samples that have been reached? Is there a way to have IPR update no matter where it's at in it's calculations, like it was way back when ?