I tried to book a train ticket from Bayeux to Paris, Gare St. Lazare, for July 18 on oui.sncf, but results came back for Bayeux to Paris Montparnasse 3 Vaugirard - several trains that day all going to that destination which I thought was different from Paris, Gare St. Lazare? Are these one and the same?
That station is in a different neighborhood, attached to the larger Gare Montparnasse, and represents a detour from the usual route - longer, more expensive, and with more transfers.
If this is a real schedule change, they've not yet informed the Germans who provide train schedules through DB. It's the kind of result you might get if construction is planned, but that more often happens on weekends on that route (and has been for a while). There could also be some issues resolved with the June 10 schedule update. I would wait a week or two before trying again.