not to bump a zombie, but 10- 20 ms off isn't enough to even hear, so why worry about it?
mine works fine, never had any issue with it a reset didn't fix.
i mean... you can't tell the diff, and honestly, to be that critical isn't gonna get out of sync enough to matter when playing with other human beings. most people's time will wander faster and slower where that amount of time is so negligible it's totally overkill to worry about for most if not all uses.
sorry to be a buzzkill, but we're talking some pretty picayune differences in time that i would bet you couldn't tell if put to a blind test. and since you can dial in the EXACT time you want anyways, seems to me there's no harm/no foul involved.
i mean... tapping 4 times in a row it is gonna average out the taps to the closest tempo YOU input. it's not crazy to think between taps you could me that many milliseconds off. seriously.
if it works, don't sweat it. it's not a long enough "glitch" to matter. if it does at all. jmo, obviously your mileage may vary. most of the guitarists i've worked with, myself included, tend to think delays sound better slightly off time anyways.
there's nothing "human" about digital perfection. peace.