Your problem might be in changed settings of Target click filters. Character Configuration > first red box on the left > Target tab > on the bottom is "Click Filter Settings"

If the target you're trying to attack isn't aggroed or engaged in any way, your abilities probably targets the last active target you've had until the mob aggroes or is attacked by someone else. I haven't checked this myself but I do remember having issues with my targeting and had to adjust that part.

Or I'm talking outta my arse and you've accidentally engaged "automatically lock on when initiating auto-attack." or you're having lag, or you have a macro in your shield lob! XD