I’m not sure how this issue could be caused by temporal optimization, but if it really is I would be surprised. I’ll look into it later. More details (perhaps a short video showing the difference with temporal optimization enabled and disabled) would be helpful.

All temporal optimization does is (roughly) count the number of lighting calculations that would’ve been done if temporal optimization were disabled, and then in the next lighting update change the lighting “cutoff” (which affects how far light is spread from each individual light source) based on that value. For example, in a more complex scene, light from each light source might be spread until it reaches 10% brightness (compared to white), whereas in simpler scenes light might be spread until reaching 2% brightness. (These cutoff values are computed before gamma correction, so 10% brightness is really 0.63% physical brightness.) Usually, more complex scenes contain many separated lights all over the screen, in which case the raised cutoff is not very noticeable.

Having this block/lighting flash issue happen and believe I found the cause, having the "smooth lighting" config enabled while also having "black tile optimization" config from High FPS Support enabled causes blocky flashing ( maybe only in dark lighting/underground? )

Yes, it seems like the bug with lightning only occurs when Black Tile Optimization in the High FPS Support mod is enabled. It also occurs even when temporal optimization is disabled. I have a fix coming in the next update. I haven't been able to reproduce the bug with zooming in/out.