The BBs pellets jammed inside of your barrel can caused that issue. There are some tips.
1. Always use the high quality BB pellets that made in Taiwan, Japan or Hongkong (Such as SRC), don’t use China made BB pellets even they look like high quality pellets.
2. Fully load your magazine and then spray a little bit of silicon spray on the top of the bb pallets, but do not spray too much, otherwise it might cause double feeding.
3. the first of the couple shots might looks strange because the bbs are flying to the direction randomly, but after few shoots they will back to normal and straight.
Hope this helps
Tim by ASGC