Calculator Works, But One Test Still Failing?

Summary:
I’ve built a calculator for the Front End Dev Libraries course. It works perfectly, from what I can tell, if overly utilitarian in its styling. But one of the sixteen tests is failing and doesn’t really explain why. Normally the failed test has a clue for why it’s failed, but not here that I can see. Do ya’ll have any ideas?

fCC’s Error Message:

14. Pressing an operator immediately following "=" should start a new calculation that operates on the result of the previous evaluation
Script error. (:0)
Error: Script error. (:0)
    at r.onerror (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:575:14032)
    at https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:584:94595
    at Array.forEach (<anonymous>)
    at te (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:584:94541)
    at n.<anonymous> (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:584:171917)
    at https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:569:259477
    at ny.Dg.run (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:569:259772)
    at r.Qg.runTest (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:569:274680)
    at https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:569:275616
    at o (https://cdn.freecodecamp.org/testable-projects-fcc/v1/bundle.js:569:274033)

My project CodePen:
Link here so you can have a look: https://codepen.io/roachy/pen/WNdQmRx

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36

Challenge: Build a JavaScript Calculator

Link to the challenge:

Any help greatly appreciated!

Solved here.