At first you have to check the GT boxes you are feeding to the network,
Considering that the data format is [x1,y1,x2,y2] which actually indicates the [left,top…] and the […,right,bottom] edge of the ground truth box, in your case :
[264.0, 632.0, 264.0, 633.3333740234375]
x1 and x2, are actually overlapping which means that you don t actually provide a box but a straight line.
As others claimed @Rmemr and @mia , you have to check your ground truth first and reassure that any zero_area boxes are discarded …