Technically the cell id recognition of the app should be quite reliable and stable. But the problem is indeed the possible variation of cells the phone is connected to over time.

I have myself recorded well over 10 cells at my home. This also covers quite a large physical area, so it can get quite inaccurate as a positioning method at least in some places.

What can be done to get the best coverage in short time is to leave the recording on and go to system settings and switch between 2, 3 & 4G manually, wait long enough and possibly also make some calls.