Custom entities' movement limited when spawned in floor.

Partner Rank: 1

Partner Team Reporting: Blockception

Verification Builds: 1.16.20

Summary: Entities spawned in the ground seem to lose movement components, and are not affected by levitation. This only appears to impact select entities.

Impact: Caused one of our maps to fail certification.

Repro Steps:

1. Spawn custom rideable/flyable entity on floor
2. Try to move using WSAD or fly via levitation with entity

Repro Rate: 100%

Observed Results:

Entity won't move with WSAD keys, nor when adding levitation to the entity. Similar rideable entities with no flying mechanic move around as expected.

Expected Results:

Entity should move around as normal, and levitate when player looks upwards.

Screenshots/Videos Attatched: Yes:
 https://www.youtube.com/watch?v=F736U2g6AWo&feature=youtu.be

Regression Builds: 1.16.10

Notes: None