Hello,
I’m Shotgun TD, here at Fortiche Prod and one of our users just reported me that he could no longer edit multiple tasks from a Grid Widget.
I managed to reproduce it by creating a Grid Widget of Tasks on a new canvas page.
Other entity types do not seem affected.
Best regards,
Sebastien Courtois
Thanks for writing in and letting us know, and sorry for any inconvenience this causes while we look for the problem. We are currently investigating another case of this so it looks like it may indeed be a bug.
Could you please send us a support ticket to support@shotgunsoftware.com and include the details of this post with your site name so we can dig in further?
Cheers,
Beth
Also, welcome to the community! 
Thank you, @Beth !
Really appreciating the responsiveness.
Support ticket submitted: #112980
Cheers,
Seb
Wonderful, thank you!
We have discovered that this is a bug that affects the multi-select right clickability on a Task Grid IF the Gantt chart is not displayed. If you display the Gantt chart, you should be able to right-click again. I recommend this as a workaround until we get it fixed properly which we will schedule immediately.
Cheers,
Beth
Just to wrap up this thread, this bug has been fixed in SG 8.13 
[SG-17875]