Could you check the updated version on Github? Check my comment here: https://github.com/mendix/BootstrapTooltip/issues/3#issuecomment-168021536
If this works, I will update it as soon as possible in the AppStore
Can confirm this is an issue on 5.21+ when widget bundling is enabled. I also confirmed this on a project with no other widgets. I posted an issue on the widget's github page.
The line that seemingly causes this issue is:
$ = tooltip.createInstance($);