No idea what it is --> Or where it came from
 
Did you flush the pump, fittings, hose & the Hydro Copper also ?
 

Either a small piece of soft tubing or part of something.   Carefully take the block apart but make sure the seals are put back into place and leak test it (12-24hrs) before firing it all up again. 

Cool GTX
I'd try to flush the GPU water block ---> before opening the block
 
Use hoses to keep the GPU dry while flushing - if any doubt let it dry before putting back into PC
 
Remember these blocks are only designed for Low pressure.  Best to use the pump (nice if you have a spare) --> your house's water pressure is too high and can damage the card seal

Is it possible to slide something into one of the ports to get to that spot and wipe it clean? 

may have to flush it or leave it.  Personally,   I'd leave it if it meant taking the block off the card.   hopefully, it will end up in the reservoir. 

GTXJackBauer
If that is plastic, it well eventually melt into your fins.

It will not melt into the fins.  The fins don't get hot.  I do agree that blockage is a concern.

If you drain the loop, you may be able to remove the outward facing port and use an old wire plastic coated clothes hanger with a piece of microfiber cloth to clean the “blob” out.

The risk you run is the wire not fitting through the port properly, the cloth falling off, or even scratching the block making it look worse. EVGA does not use an intricate pass through design like most other companies. Their flow channel goes directly in through the port, over the vram, through the pass through over the core, over MORE VRAM AND SOME VRM, then directly out of the other port, so it is definitely 100% possible.

You may have better luck gently taking the block apart and cleaning the plexus part with a microfiber cloth. It is much less risky, and won’t take all that long. The longest part will be verifying that the o-ring is properly placed so that it doesn’t get pinched or cracked when reinstalling the block.

Highly doubt it would melt.  It's constantly being cooled by water.  

If your CPU core is 75 degrees celsius, how hot is the fins/micro channels? Less than 75 degrees celsius. Let's say 60 degrees celsius (15 degrees delta T between Tjunction and die, paste/solder, IHS, thermal paste/liquid metal, block, cooling fins/micro channels). Very generous for you. What temperature does acrylic melt at? 160 degrees celsius. What temperature does PETG tubing melt at? 235 degrees celsius. What temperature does PVC melt at? (the most cheap and crappy of tubing) 100 to 260 degrees celsius depending on additives.

None will melt at 60 celsius.

You must have been using the cheapest of tubing, had complete blockage in that section of the block with all water evaporated/air pocket, and the CPU must have been running 105 celsius for many minutes.

I would say that it is way more likely to not melt than to melt.

the topic is the thing in the clear acrylic.  That you can see.  surrounded by liquid.  That cools the thing.  That you can see.  That even if it did get in the fins,  small enough not to melt.     If you wanted to get at it, maybe open one of those ports and used a curved paperclip or something to retrieve it.