With the latest version of both Immersive Portals and Simple Clouds, rendering errors occur whenever an immersive portal is rendered and shows the overworld. All blocks within the nether, the dimension that I was in whenever this error occurred, will become pitch black whenever the immersive portal is on screen/rendered. However, I was able to see the overworld through the immersive portal without any issues. Additionally, if Immersive Portals is installed at the same time as Simple Clouds and a single-player world is joined, both mods must be disabled or uninstalled in order to rejoin the world, otherwise, you will get the error "Internal Exception: java.lang.IllegalStateException: End size 239 is less than fixed size 240" and be prevented from joining. (the number values are seemingly random without further information, as the number values are not replicable.)

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https://mclo.gs/6zpOto5 Logs, in case they would be useful in resolving any incompatibilities.