Unable to resize columns

[Welsh Mark3]

This issue is a little difficult to describe, essentially it seems like I am unable to resize columns and in some instances unable to select a column or row. The formula drag function also does not work. There also seems to be a delay when moving my mouse pointer, only seems to happen in excel.

We have recently moved to O365

Has anyone else experienced this problem and know how to resolve it?

 

[Joe4]

Is it with all workbooks or just certain ones?
It sounds almost like there is some sort of worksheet protection being invoked.