London-Shanghai-Tokyo-Shanghai-London, am I eligible for the 144-hour visa free transit?

Hi all, thanks for taking the time to read my question!
As above, I am planning on stopping off in SH twice during my trip to Tokyo. The first time will be at the start of the trip for 4 days, and the second will be at the end for 3 days. As such, my itinerary looks like:
London-SH, SH--Tokyo, Tokyo-SH, SH-London.
I think I qualify for the 144-hour visa free transit for my first stop in SH, but would I be able to get it again on my return? Is there a limit to how many times you can get it?
Many thanks!