Bands run at the edges of the gel can often be distorted; it's a common problem but mostly a cosmetic one (the bands usually still migrate properly). You could try loading the gel without using the edge lanes if possible. Depending on the sample volume you need to load, you could also switch to a 15-well gel to avoid using the edge lanes while still running 10+ samples.

Thank you Aaron for your suggestion! I'll try to load in a different well next time.

You can reduce the time between the samples loading. and prepare all the chemicals in HPLC water. One more important thing is to shake well before using the running buffer. The concentration of the sample and sample buffer should be the same. This troubleshooting will solve your problem.