I never used Tasker, so I can only guess, but mobile cells are usually identified with four numbers: mobile country code, mobile network code, local area code and cell ID. Given that these are the numbers that are available for mobile cells, Tasker has to somehow derive these numbers from the ones I mentioned. I have no idea how, because I don't know the cells around you (and around here most of the cell IDs and local area codes have 5 digits. You can check yours too, with some other app, I use OpenSignal, which can give me the LAC/CellID).
As far as I know that 4321 can't be the mobile country code (it would be 3 digits, 432 is Iran) or the mobile network code (3 digits at most, only 2 digits in most countries), so my guess it that it's your local area code. And the other number after the period your cell ID, maybe. If my assumption is true, then it could mean something like that the line with only your LAC makes the app detect the local area with the mobile cells visible from the given area. It would mean that if you include the line then the app would think that you are in that local area even if you don't see any of the cells that you usually do when you're at the location, but you see cells from the same local area. That could mean being miles away. The maximum range of a GSM cell can be as much as 35 km. And if removed it could mean that the app would detect that you are not in the local area in the moment it can't detect the nearby cells temporarily for some reason. (Which can often happen.)
But this is just a guess.
Another guess is that 4321 is indicating byte order for some identification number (maybe one of them mentioned above). But then I have no idea why would the app behave like it was described.