I’ve sometimes had this and other issues when Symettry is turned on. With it turned off I have no issues and when finished Topo I just mirror and weld.
Dillster is correct. Sometimes slight variances crop up from side to side, causing targets to be missed when symmetry is on. Mirror and Weld fixes most problems, to the extent I rarely bother with symmetry at all during retopo.
thanks, you both were right