Being a video game series, Red Dead Redemption 1 and 2 are bound to have some glitches. I've had some pretty weird and funny glitches myself which consist of:
In the last mission of "Idealism and Pragmatism for Beginners" after kidnapping Jean-Marc and bringing him to the mayor's mansion, I must have dropped him in a wrong spot or something before the cutscene triggered where Jean-Marc was completely invisible during the entire cutscene while Arthur and Henri Lemieux acted like everything was normal. However, Jean-Marc became visible again after the cutscene ended at the part where you choose whether to kill him or not.
A similar glitch happened in the side mission "He's British of Course" after capturing the "Zebra" and bringing it back to Margaret, the model for the "zebra" glitched out during the cutscene where it was doing this demonic looking walk leaving Arthur and Margaret to appear to be mimicking leading it back into the cage. The zebra/donkey appeared in the cage like normal after the cutscene ended.
Once in a while a carriage or wagon wreck will just randomly happen sending the wagons flying at absurd heights which is pretty funny to watch.
I haven't got many glitches so far, but I would love to hear what glitches all y'all got playing your games.