Did you tram your wasteboard with your spindle? That sounds like either a sloped wasteboard, or an out of level X axis boom. Your X travel and wasteboard must be coplaner.
With the machine on, get a set of feeler gauges and move the Z carriage to then end of the X axis with the “gap”. Lower the bit until you can justttt get a .02" feeler under it. Then slowly jog it to the other end of the X and see if the .02" feeler still fits. If not, you’re table isn’t parallel to your X. You could fix it by tramming your board, or by leveling your X boom (I’d go the latter, if it’s significant)