mentioned, you need to probably make some adjustments to your configuration to make things work in Lightning. As with any transition, the most important work - planning and analysis of the existing implementation. In Salesforce you can use the Lightning Experience Transition assistant to do the analysis for you. Access it from Setup -> Lightning Experience Transition assistant -> Discover Phase -> Point 2 -> Click on "Check Readiness". It will generate report for you which will tell you - Why move to Lightning? Benefit of it, which of your existing implementation is good to move to lightning and also where you need to do some changes. Each recommended changes will show you the guides to help you to do the tweek and also how much effort needed. That way you can plan.

I would say use this tool against your production instance to get correct picture. Sandboxes are not always up-to-date.

Any problems, please let me know. Thanks.