So Since I put the BL touch on this printer, my Biqu B1, I’ve experienced some of the problems you read about but one that comes up that I see is that even after it’s apparently working the first layers still don’t go down flat and adjusting Z offset is impossible because some area will be too close and some too far away.
On my printer, I followed some instructions to make sure the vertical Z-axis extrusions were parallel, and after I finally got the bugs out of everything else it worked perfectly for a long time. I’ve recently had to work on the bottom of the printer and having it rest on the edge of the base and the Z extrusions for support, it knocked it out of alignment. I knew what it was but today I had to change out my bed magnet so I did a bunch of work at once and probed a new mesh and once again the first layer is perfect.
All of this to say that if your BL touch is not seeming to level the bed properly, check the Z extrusions to be sure they are perfectly parallel. if it isn’t the X-axis will corkscrew and the BL touch will not be able to compensate for that