Unexpected instrumentation error logged with debug mode enabled

[jzaefferer]

When calling Sentry.init with debug: true,, Sentry logs a lot of these errors:

 ERROR  Sentry Logger [error]: Error while triggering instrumentation handler.
Type: xhr
Name: <anonymous>
Error: [TypeError: Cannot assign to read-only property 'lastIndex']

This disappears when disabling enableAutoPerformanceTracing.

Any idea what's causing this? Or how to debug this further? Would be helpful to get a stacktrace for the underlying TypeError, but I don't know how to access that.