Have you tried to run your pump closer to your cold trap. That looks like a pretty long run for a gl connection.
If you really want to find where your problem is. Helium is an easy way to find your source of the 120 micron. I personally think it’s low enough especially for a Chinese GL rig, but you could always spend $16 on a tank of helium at Walmart and check everything. That vac line looks long though.
Did you check what your pump was capable without the short path??
And if this is your first time. I suggest you find a way to throttle your vacuum if needed. There are several members here including myself that have pulled oil from our BF threw our heads. Looks like you spent a deceit amount of money on that setup. What’s a few hundred more??