Flickering shadows for custom entities

Summary: Custom entities in Wildlife: Jungle have flickering shadows.

Verification builds: 1.12.0.5

Impact: Custom entities have flickering shadows. At some times the shadows look normal but often times they are flickering.

Repro Steps:

1. Load Wildlife: Jungle world template.
2. Spawn any custom entity (e.g. jaguar).
3. Watch the shadow.

Observed Results:

The shadows are flickering.

Expected Results: The shadows shouldn't flicker.

Screenshots/Videos attached: Yes

Notes: I am experiencing this on my Windows 10 computer. But when tested on a different computer with the same Minecraft version, it doesn't happen. So it might be quite unpredictable.