This may not be a bug and may be a legit change but I've dealt with it since Jets launched last May and it's still not been fixed which makes me thing it's a game tweak. That said I'd rather ask than keep dealing with it if really is a bug ( I know a lot of people on KOTH servers complain about this as it's made the hand carried AA less likely to be carried into battle).
I've found the Titan AA much harder to use outside a very specific set of ideal conditions since Jets DLC. Prior to Jets DLC it was easier to maintain a lock if a jet ducked behind a tree/other for even a split second. Now even a fraction of a second behind a tree or other cover causes me to loose my lock and or restart lock acquisition.
Furthermore prior to the DLC it was easier to maintain and acquire a lock as the jet moved as the system was more forgiving if the target strayed from the viewfinder. Now if the jet leaves the inner 50% circle (or so) center of the crosshair I loose lock acquisition and/or lock all together. Previously once a lock was acquired you only had to keep the view finder in the ballpark of the Jet.
This makes firing at jets that are moving adjacent/perpendicular to my location much harder at close range. At long range a jets flares make it all but impossible to achieve a hit so now the AA is only effective if a jet is moving either directly towards, away, slowly, or the observation point is ideal. While not a deal breaker I've adjusted my tactics, but still find this frustrating as it's made the in the field AA launcher less useful.
I was hoping this was a bug but it's been a year and given what I noticed with the AT launcher I thought I'd log it to find out.