@Falcon_ You are welcome fren. I have looked at the handling but couldn't spot a problem, of course I may have missed it too.
What can I suggest you is, backup this not working handling.meta first (just in case), then download that mod again and extract it's handling.meta (You can simply put it's dlc.rpf file in the main gta directory and extract the handling.meta afterwards. Change it's name to handling.meta - original so you don't confuse them).
Then you can download this https://notepad-plus-plus.org/downloads/ . Once you install it, go to Plugins > Plugins Admin . Search for Compare and install it. Notepad++ will restart.
Then open up both the faulty and original handlings and go to Plugins > Compare > Compare. It will show you all the differences between them. I believe there is an error with one of the lines.
If that's the problem, just correct those particular line codes in your faulty handling.meta by looking from the original one.
If the only differences are your custom values, then I'm gonna need a screenshot of the comparison so I can look at which values you changed and check can they cause any problem.
As a question by the by, I saw the jet using custom weapons.
Have a check that these 2 weapons are included in a custom weapon meta (Not exactly sure how it's file name could be but it should be a different file than what an addon car include).
If there is no file containing any data with those weapon types, check the descriptions of the mod's download page. The author might have give a link for a different mod that includes custom weapons.