Errors on a console on upgrading a project from 2017.3 or earlier version to 2019.1.0a9

Steps to reproduce:
1. Create a project in unity 2017.3 or earlier version
2. Save and close unity
3. Open the same project on Unity 2019.1.0a9
4. Accept the dialogue regarding updating version

Actual result:
Observe errors in console regarding Ignoring asset refresh.

Expected result:
Project should import gracefully without any errors

Reproducible on :
2019.1.0a9

Works on:
2019.1.0a8, 2018.3.0b10, 2018.2.0f2

Environment:
Windows and Mac

Note:
1. Works fine when project is upgraded from 2018.2 and 2018.3 to 2019.1.0a9

Error Details
1. Ignoring asset refresh of 0000000000000000a000000000000000 because the file or its directory couldn't be found!

2. Ignoring asset refresh of 3c0ad459c1534645b5d603b7cc258f97 because the file or its directory couldn't be found!