Visually all my mekanism cables/fluid/item/power transports are broken....
I can break them and place them again and it all good for a while, but eventually returns to a broken looking cable...

seems to function fine...
but it makes me not want to use this mod

I'm using the most recent file I could download for 1.16.4

duplicate of #5922 short answer is remove immersive portals, the mod is not fully compatible with forge and breaks various forge systems that mekanism relies on.