Dangers of importing project from old version of Unity to newer one?

Is there something possibly insidious about opening a project from an older version of Unity in a newer one? I'd like to take advantage of some new c# features, but I don't want to risk having something not porting over correctly. Has anyone caught anything unexpected that changed after updating to a newer version? Coming from Unity 5.5.0b11 to Unity 2018.3.11f1.

 

- make backup and then a backup of backup
- you will have multiple pain points you will need to get through, the most important is the new prefab system and probably you will need to reimport the majority of your assets

Do not open your project in newer version without proper and full backup. Ever.

 

I'm more worried about subtle changes to the physics or similar that might alter the feel of my game without my noticing. Probably being paranoid, but I figured i'd see if anyone experienced anything like that. Not too concerned about visual asset translation.

 

Also if you have assets in your project like TextMeshPro and ProBuilder that have moved to the package manager, look for special instructions for how you convert these.

 

Well, Physx has been updated since then... but I have no idea how different it is in practice. I haven't noticed anything substantial, but I have never worked on physics based mechanics seriously, so I haven't compared them.

I'm pretty sure you will find some things which is different, a code base this big, a time gap this great will deliver differences. Just make a backup, upgrade, fix and test. I don't think people will answer this question meaningfully.

 

I would say it is very likely you will have issues and behavior changes. If you really feel like doing it, I would do it in several steps, like maybe upgrade to 2017.x first, etc so you can identify which Unity version is causing you the problem.