Program stalls when it runs to an end.

Hi, everyone, I am new here.
Recently, I adopted prophet to do some forecast in stock market. It goes smoothly most of the time, but I encounter some problems from time to time because my program, specifically, one of the processes (I should mention that I use multi-process to accelerate the speed) seemed fail to exit after running to the end. It seemed to relate with the workload because I hardly encounter such problem when the workload is low (ie, fewer iterations on my parameter space), but it appears more often when the workload is relatively large.
In addition, I initially ran my program in Jupyter Notebook, so later I ran that in the Linux terminal and I found that such problems reduce by some degree but it still occurred some time. I am quite confused and bothered about this, can anyone help me out? Many thanks!
My backend is pystan, as is suggested by the author, maybe related to some faults in pystan?