I am assuming that you tried this on 14-Dec-2017, based on the Start Date you have provided above.
Looks like you have a difference of 2 years 2 months and 15/16 days between the first two tasks and the last three.
So, it appears that when the Project was created on 14-Dec-2017, that shift of 2 years 2 months and 15 days got translated into the last three tasks.
Easy way to verify would be to:
1. Create a Project with a Start Date as 1-Jan-2017
2. The expectation would be that the last three tasks have a Start Date of 15 or 16-April-2020.