Popup on the modem login page?

[wireless]

I just went to log into my modem to check some settings and there was an extra popup login window that I have never seen before. I obviously didn't enter any info, just closed it and logged into the modem normally. Is this something to be concerned about? Windows Defender has never found anything, Malwarebytes found nothing, and once every few months I will install antivirus to check which has never found anything either.

Here's the popup:
https://bhzof35755.i.lithium.com/t5/...e?v=1.0&px=999


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