I had similar issues with the 1st layer being inconsistent across the bed area, documented here: Z offset irregularities across the build surface - General / LulzBot TAZ - Lulzbot
Ultimately I gave up on the printer. Personally I would not buy a printer without mesh leveling with some kind of sensor, which is a common feature on printers nowadays. I spent a huge amount of time coming to this conclusion, and I hope I can save someone else time, money and frustration.