Datacursor custom UpdateFcn working in 2019a but not in 2020a

I created an appdesigner app in 2019a where I set up a structure s.DataTipTemplate.DataTipRows with the tooltip info I want to display. My UpdateFcn 'lookup' returns the tooltip text and also reads from a log file and displays it in the app. I apply this using

dcm = datacursormode(app.UIFigure);

dcm.UpdateFcn={@lookup,s,app};

This works perfectly in 2019a. In 2020a, the tooltip seems to be displaying correctly but the log file is not being displayed. I tried adding fprintf statements to 'lookup' but they are not displaying. I am having a hard time debugging this since breakpoints don't work in the lookup function and printing doesn't work either. Is there something wrong with my approach? Thanks