This has been working fine previously, and I've checked the changelog for breaking changes but found none: When the scheduler view contains a block appointment, onActionFailure is triggered and no appointments are displayed at all:
kycdock-ej2.min.js:9 Uncaught TypeError: this.parent.getHeaderTooltipTemplate(...) is not a function
at t.e.createBlockAppointmentElement (kycdock-ej2.min.js:9)
We have checked the reported scenario in latest version and event are displaying correctly with block interval and tooltip combination. Kindly try the sample and if the issue persists, try to reproduce the error in a sample and revert else share build version, your template code example (with JS code) /runnable sample (if possible) to serve you better.