solution on the time domain becomes “periodic” after the inverse fourier transform
Multiplying a kernel and signal spectrum in Fourier domain lead to a circular convolution and not a linear convolution, so in order to it become linear convolution you must zero pad your signal and kernel before taking the Fourier transform (up to M+N-1 where M is the signal's length and N is the kernels's length). (if you compare the blue and orange signals, the beginning of orange signal has higher values because of of higher value at the end of blue signal and it has lower values in the end because of lower values in the beginning of the blue signal).