I'm not surprised about the trailing, if I'm honest. I use a 5D IV for astro occasionally, and I've found that when I have proper focus, the rule of 500 is not enough. I would commonly use a 14mm f/2.8 open for 30 seconds on a 6D and be satisfied with the results (albeit maybe with less than perfect focus), but I've found that with the same lens on the 5D IV I am hesitant to even go for 25 seconds - much better results at 20 seconds when focus is bang on. I'm pretty confident that I don't have any movement anywhere, but 30 second exposures have noticeable trails when really looking. Maybe 30mp on a sharp lens is just a bit too long for the rule of 500.
By the rule of 500 you should be able to get 14 seconds from a 35mm lens, and I should be able to get >30 seconds on the 14. In practice, however, it seems that from my experience maybe the rule of 350 is more accurate.