If you change your resin the reading should drop to zero within a couple of minutes (if not quicker) of turning the water back on. Does with my 200GPD RO-Man.
If you have an inline TDS meter I have noticed that it does not read the same as my handheld, only + or - 001 though, not as much as your reporting. Judging by comments made on this forum I would trust the handheld reading over the inline meter.
Do you have any way of checking your handheld meter is working properly? Calibration solution perhaps? You're in the dark if your meter is playing up. Had it happen to me with my first one. I was sold a duff one which would not read less than 055.