Eh I would say it’s got to be how it’s mounted. I would never trust an optic mounted into the rear sight notch. Unless you get your slide cut for your optic or have a plate to attach the optic to the slide I can assume you’ll have some issues holding zero
Your options, outside modifying the mount, are: -Exchange it, and hope for a new one that is made properly. -Return it, and have the slide milled out to accept your RDS. -Find a new mounting solution. -Forgo adding the RDS.