Hi Nicole and others...
We have identified the issue that's causing the delays. Applying the touch-action style to several elements seems to cause Chrome some issues. In the Boost theme, Bootstrap version 4-alpha is being used. In the _reboot.scss file (line 263), touch-action: manipulation is being applied to several elements to prevent the click delay that some browsers don't remove when using meta content="width=device-width".
If you reset the touch-action on these elements (to "auto") within the grade book, the delay is gone. I believe it's Chrome that is ultimately misbehaving but I don't believe it will be corrected anytime soon.
Attached is the fix we are deploying to resolve the issue in the grade book. I will be making a tracker issue soon.
Hope this helps!