Please note that the Login form widget is outdated and no longer needed in the newer version of the platform. You can now model you login page with standard mendix components.
Have you upgraded your widgets and cleared your cache memory?
We had a similar issue that was resolved by using the newer login componentry provisioned in mbm. Again...just write something that interrogates the headers from the browser, make a regex comparitor, and present the user with a screen that tells them to download a proper browser, that actually fixes that problem, believe me
Did you perhaps install or upgrade the pushnotifications module to the most recent version ?
I had the same issues in IE 11 after doing so and they are caused by typo’s in the pushnotification widget.
See my review of the pushnotifications connector in the appstore.
You can only reproduce the errors locally when you check “Bundle Widgets When Running Locally” in the modeler .