To resolve that error and several others that came after it, I found that I needed to manually make my server add a Content-Encoding: gzip
header to three files and a Content-Encoding: application/wasm
header to one more file.
For WPEngine, here are the four Header Rules that need to be added under the environment's Web Rules:
Set > Content-Encoding > gzip > Only on successes > URI = /MYFOLDER/Build/MagnetAtomic_Build.data.gz
Set > Content-Encoding > gzip > Only on successes > URI = /MYFOLDER/Build/MagnetAtomic_Build.wasm.gz
Set > Content-Type > application/wasm > Only on successes > URI = /MYFOLDER/Build/MagnetAtomic_Build.wasm.gz
Set > Content-Encoding > gzip > Only on successes > URI = /MYFOLDER/Build/MagnetAtomic_Build.framework.js.gz
Replace MYFOLDER with the correct relative path for your website.
Some of the headers were being aggressively cached by Chrome even after I tried all of the usual cache-busting methods, so I had to completely close it before it would recognize the new headers.