Under some circumstances the patron entry form and toolbar are not displayed by memberentrygen.tt. For instance, if there are no libraries or patron categories defined. If this happens a JavaScript error is triggered because a check for #toolbar's position returns null.
It feels like this could only happen if you work with the db user and have managed to not create the values in the installer (onboardig) somehow - should we mark WONTFIX?
This turns out to have been fixed by the switch to the hc-sticky library for floating the toolbar. It doesn't throw an error when the toolbar doesn't exist.