Can't use object mask in v26 (Windows version)

This issue remains elusive to reproduce in-house but we have made some changes in Beta to attempt to resolve this issue. If you can try the latest 26.5 beta and give us you feedback it would be appreciated.

They have significantly changed the way we user set masks now in the 26.x release. There are two different modes, frame and clip ... and they differ in how to set them and what they do. You probably should go to their help files on masking to get this sorted out.

Thank you for your reply

I have selected the clip and click the "Show Object Hover Preview", but I still can not see anything was happened. 
I also can not use the "pen mask tool" to make a mask on a clip. 

@Leonard0987,

You have the Object Mask Tool selected with the lasso option, and you are hovering over the Program Monitor. That is correct.

Do you have a clip selected in the timeline? If not, it won't do anything.

If you do, click on the Lasso/dropdown to the left of the + sign. Do you have "Show Object Hover Preview" selected? If not, it won't show you the objects it detects.

Stan