Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.

I have encountered a very strange bug.

After leaving a Babylon scene open overnight, it had frozen, with the following error messages in the terminal:

Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:14884
Error: WebGL: drawElementsInstancedANGLE: Extension is lost.libs.pkgd.js:9:17107
Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:15419
Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:14884
Error: WebGL: drawElementsInstancedANGLE: Extension is lost.libs.pkgd.js:9:17107
Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:15419
Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:14884
Error: WebGL: drawElementsInstancedANGLE: Extension is lost.libs.pkgd.js:9:17107
Error: WebGL: vertexAttribDivisorANGLE: Extension is lost.libs.pkgd.js:9:15419
Error: WebGL: No further warnings will be reported for this WebGL context. (already reported 32 warnings

When I refreshed the page, the same errors kept appearing, until I restarted my browser. Has anyone seen anything like this before?

Note: The scene is periodically creating and destroying instances. When the instances are destroyed, .dispose() is called on them, which I assume is the proper way to destroy an instance.