I faced this problem where I used a new flash trigger and after a couple of good photos, photos started appearing like this https://imgur.com/a/iNw4rkr then the camera stopped working for a while and when it did there were two lines following the f stops. so I tried the old trigger and had the same problem, after a while I realized that the shutter was 1/ 400 and 1/250, and when I slowed it to 1/100, no problem anymore.
The flash can only operate if the entire shutter is open for a moment. At shutter speeds above about 1/250 second, the second shutter curtain drops before the first is all the way at the bottom.
Your camera will list a shutter synch speed. That’s the fastest you can shoot and fire a flash.