Do you use Java 8?
Yes

What version of Minecraft do you use?
1.12.2

What version of MinecraftForge do you use?
14.23.5.2814

What version of Immersive Engineering do you use?
0.12-89

What version of Immersive Cables do you use?
1.3.2

What is the issue / bug you have encountered? Give us a short description.
When i place quartz fiber connector to AE2 cable, and destroy it, the cable still renders near the point where quarz fiber connector was connected. There is screen shot:

How can it be reproduced?

1. place any 8 channel ae2 cable
2. attach quartz fiber connector on it
3. destroy quartz fiber connector

No logs.

I'm developer of Applied Integrations (addon for AE2), i have encoured this issue in alpha version of my mod. You can fix it, by overriding method which called on tile destroy. You should put something llike this in your connector code:
@Override public void invalidate() { super.invalidate(); if (world != null && !world.isRemote) { if (gridNode != null) gridNode.destroy(); } }

P.S. I know about pull requests, sorry i don't have much time to create one :c

Some additional info:
I didn't encoured this issue for any other AE2 or RS tile from your mod, transformers is working fine, and they don't cause this issue

Every connector overrides TileFluixConnectable, which does destroy every connected node on invalidate().

After looking over the code I noticed I forgot to destroy the outerProxy in TileConnectorQuartz. I'll see if that really is the issue and fix it in the next update.