This is typically caused by the gel overheating. I would reduce the voltage and perhaps also check that your buffer is the correct composition.

See a previous RG answer:

https://www.researchgate.net/post/Why_do_my_gels_have_crescent_smiling_effect

Dear Stephanie Xue

Please check the gel tank carefully. There is a thin wire on the upper side which run across the tank. Make sure it is in its proper position. From the picture it seems that the wire is slightly moved from its actual place on the right hand side.

I hope it will help you. All the best.

Before you load your samples make sure that your gel is same size and thickness from all sides

run your gel lower voltage and less time and the samples will be a thinner band and no risk of them going off the end of the gel

That means the electrical field is not homogeneous across the gel, often because the running voltage is too high and heat dissipation is better toward the edges of the gel, as others have mentioned above. However in your case the running front 'warps' to one side only, so you could have a warped electrode or a poorly designed electrophoresis chamber. Also, did you ensure that the gel was cast on a perfectly horizontal surface and/or that the chamber sat on a perfectly horizontal surface? Differences in height across the width of the gel, or in the depth of the buffer layer covering the gel might also account for what you see.

Hope it helps!