Hydrogel-like fluid vs blood plasma

This gel-like liquid has been appearing in my LBA tests for a few months, usually in the middle of the slide. I think it's because it's denser than blood plasma, so it sinks to the slide immediately when the blood drop is taken. At first, it's just a spot, but then it starts to spread. (I could still see it spreading a day later.)

Sometimes, it covers a group of RBCs or WBCs. (See pictures below.)

Karl.C also posted a video about this fluid.

In my most recent LBA, I was able to record an interaction where the liquid covered a few RBCs, and in the process of spreading, it enclosed a small area of blood plasma that also contained RBCs.

The interaction between them at the contact surfaces (left side: blood plasma with RBCs, right side: gel-like fluid with RBCs):

While spreading, it often covers RBCs. Here you can see the blood plasma island. The arrow indicates where the interaction happened:

Mag 40x:

Spreading (6 hrs later):

Here is a half-covered WBC: