I am using Excel 2016. In one of the worksheets, I have an ActiveX combobox that contains some city names. The city names are populated when the workbook is loaded. Everything is fine up to this point. But after I click on the combobox to change the city, I cannot change the value of any cell in the worksheet. it is like the worksheet is frozen. If I go to any other worksheet then go back to the concerned worksheet, everything works fine.

Then, I added empty Combobox in every sheet. The same thing happened once I click on the comboxbox. And again, the problem disappear when I leave the sheet to another one and go back.

I do not know what I did wrong. Note that I tried this on a clean workbook, the problem did not occur.