One cause is excessive flux burden (the amount of flux deposited). Excessive flux burden can cause weld bead distortion, as well as pockmarking and porosity. Inconsistent weld toes and rough weld ripples, known as chevrons, stem from the weight of the excessive flux.
Flux burden should be deep enough to prevent welding arc flash-through but still allow the operator to see the bottom of the contact tip. If you are using the shroud-type flux nozzle (which surrounds the contact tip), then measure the distance from the bottom of the contact tip to the bottom of the flux shroud and subtract that value from the predetermined contact-tip-to-work distance (CTTWD). This value will be the bottom of the shroud to the bottom of the weld joint or surface.
https://www.thefabricator.com/thewelder/blog/consumables/improving-results-in-flat-position-submerged-arc-welding