The Wandering Trader runs with a very high velocity and he doesn't stop if there are no walls to block him. If you hit this Wandering Trader he still runs, but slowly. After five seconds he goes Sonic again. I hit him four times off screen and he literally does not want to stop running at this extreme speed. Relogging into the world made him dissappear for good.

I'm sorry but the video length/size does not fit into the attachments so I have to send you a YouTube link instead: https://youtu.be/W_x_d1ASR-w

I don't know why it happened, but I think it has something to do with setting difficulty and time. I did not modify his attributes nor gave him any effects. This happened on the Optifine mod for 1.14.3 but I believe this is not the issue. I am sure this also occours on 1.14.4.