Web site route creation missing

🚧 THIS IS A TICKET MIGRATED FROM UPVOTY. The original ticket and comments will be available for a limited time over at:
https://abrp.upvoty.com/b/report-a-bug/web-site-route-creation-missing/
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The web page is not allowing me to plan any new routes.
This started after i started to use the 'my drives' feature & clicked the 'back' button. After that nothing.
No amount of cookie clearing, cache clearing & hard reloading is helping.
It was working in this browser on this particular computer before today. It is still working normally on my phone & in edge browser on same computer.
Cheers
Nick