Changing the status to Untriaged, so that the issue would get addressed.
Thank You.

This is the design issue of the Google's app chooser (I don't know the
exact product name).  The browser / rendering engine does not guarantee
that the hover border will be drawn at least 1px width, so if the zoom
level is under a certain threshold it is possible that the border becomes
sub-pixel and will not appear.

This is not only new tab page, but the www.google.com proper shares the
same issue (because the widget shares the same code?).

Can someone in NTP team confirm this and determine whether this is worth
fixing?

I don't think we (Chrome NTP) can do anything reasonable about this. If it's good enough for google.com, it should be good enough for us.

If anything, I guess we (Chrome) could consider improving our rendering at small zoom factors, so that things scale more gracefully and don't just disappear. But still, at some point there just won't be enough pixels to do anything useful, and anyway it seems like a lot of effort for little gain.

So overall I'd just close this as infeasible.

As mentioned, probably infeasible. Please reopen if you feel differently.