With VanillaFix 1.0.10-99 and BetterPortals 0.3.5, not being in the dimension visualized in a portal causes particles to stop spawning and animated textures to stop animating.
Shown here: https://imgur.com/eXCsac8

I originally thought Optifine was the cause, but after disabling everything but BP, Forgelin, and VanillaFix, it turned out VF was the issue (thanks for pointing me toward it as the cause for this one). Optifine works correctly, even with Smart Animations turned on.