Some striders may spawn floating in the air. Although they are perfectly rideable the game thinks the strider's position is on land causing it to become purple and walk slower. It looks as if this strider is walking on some kind of invisible blocks...
Linked issues
is duplicated by 27
Attachments
Comments 4

Yes, I have started this world in 20w17a, but i'm pretty sure that I only loaded those striders in during 20w18a but i'm not to sure...

It appears that the striders from previous snapshots have kept the NoGravity
tag. I have experienced this too after opening a world from 20w17a to 20w18a.

@violine1101 I made it before 20w18a
Did you generate this world in 20w18a or is it possible that these are leftover striders from 20w17a?