When getting heatstroke in the Nether, the screen goes black while looking towards the Nether portal with Immersive Portals installed:

If I were more experienced, it could be possible to collaborate with the developer(s) of Immersive Portals on this issue, but truthfully I don't know much about shaders at all. The blur shader that Cold Sweat uses is basically just the Vanilla one.

That leads me to believe it is something they may address on their end, as any mod making use of vanilla functions would encounter the same problems and supporting said functions would greatly improve mod compatibility.

Your insight is much appreciated, I'll be following their issue to see what becomes of it, thanks!

I see, thanks for the heads up - will close this in favour of the existing issue(s).

No problem. Best of luck :)

If this is something that needs fixing on their end, let me know and I'll report it on their tracker, thanks!

This looks like the same issue as #490. The easiest option is to just disable the blur effect. Minecraft's shader system isn't perfect, so it isn't unheard of for it to conflict with mods that do more advanced rendering.