Error loading webview - Could not register service worker: InvalidStateError

[raffian]

I've been using the extension for over a year, no issues until now.
Alt-D stopped rendering diagrams, this is the error I get.

Error

Error loading webview: Error: Could not register service worker:
InvalidStateError: Failed to register a ServiceWorker:
The document is in an invalid state..

What I tried

• Cleared VSCode code cache
• Uninstalled ext 2.17.5, reinstalled (no change)
• Downgraded to 2.17.4, same issue

Config

PlantUML Ext 2.17.4/5 (no other plant ext/viewers)
VSCode: 1.82.1
Windows10 x64 10.0.19045
Java 8/331

    "plantuml.commandArgs": [
        "-server",
        "-XX:ReservedCodeCacheSize=240m",
        "-XX:+UseConcMarkSweepGC",
        "-XX:-UseCompressedOops",
        "-XX:-UseCompressedClassPointers"
    ],
    "plantuml.java": "C:\\javatools\\java\\jdk8-331-oracle\\bin\\java",
    "plantuml.previewAutoUpdate": false,
    "plantuml.render": "Local"

[raffian]

Rogue instance of VSCode cause this issue; simply killing the process from Task Manager solved it- (embarrassing).