I'm afraid that the described issue is a bug, and you can find it logged in our issue tracking repo below:
I'm afraid that there's no applicable workaround for the time being. Even if there was, it should have been manually applied in the spreadsheet instances, which is duplicating the effort of altering the IF usage with the ISBLANK.
Having in mind the heavy data scenario that you have at your end, and the critical severity of this bug at your end, we will try to escalate its priority and evaluate whether we can come up fast with a fix.
In addition, I have updated your Telerik points for pointing that issue out.
Please accept our apologies for the inconveniences caused by this bug.
Get quickly onboarded and successful
with your Telerik and/or Kendo UI products with the Virtual Classroom free technical training, available to all active customers. Learn More.