This might be the origin of your issue, or at least an allusion to the clue behind the actual reason for why the vehicle add-ons within your resource are crashing your FiveM client.
See these posts:
[Release] Auto Merge Vehicles - #43 by Jamelele1
[Release] Quickly merge vehicle .meta files - #54 by Lupin_III
These posts and the information they provide should at least be allusive towards the potential inconveniences and dangers of merging your vehicle add-ons’ .meta files. Personally I don’t believe that anyone should be attempting to install any vehicle add-on in this particular fashion, regardless of how convenient this method may actually appear to be. There are other ways that I believe are significantly more convenient to install vehicle add-ons with than the aforementioned one.
Of course I don’t entertain that particular method of installing any vehicle add-ons within my own resource myself, but that still doesn’t mean that there aren’t other alternatively available methods that you are able to attempt.
Even then, you really should opt to install each vehicle add-on within your resource in a more linear or intuitive fashion as I’ve done in order to minimize or even eliminate the possibility of crashing your FiveM client on behalf of a problematic vehicle add-on. I’m willing to help you do that myself, and shown below is the way that my vehicle resource is structured.
Personally I find it far easier to individually install and manage each vehicle add-on within my resource itself, because I not only have total control over the installation and management of the add-ons themselves, but also the potentiality itself of any issue(s) involving them that may manifest within my server.